Preparation and application of multi-dimensional s-doped manganese cobalt nanorod / n-doped carbon nanosheet composite

Abstract

This invention discloses a method for preparing a multidimensional S-doped manganese cobalt oxide nanorod / N-doped carbon nanosheet composite material. First, carbon aerogel is prepared using chitosan as both a nitrogen and carbon source. Then, it is activated and carbonized with KOH to transform into two-dimensional N-doped carbon nanosheets. Next, the abundant nitrogen- and oxygen-containing groups on the N-doped carbon nanosheets are used to coordinate with metal Mn and Co ions, ensuring uniform dispersion of metal ions on the carbon nanosheets. Finally, sulfur powder is sublimated to generate sulfur vapor, which reacts with MnCo₂O₄ to produce S-doped MnCo₂O₄. This invention uses biomass chitosan as both a carbon and nitrogen source, and is simple to operate and low in cost. The prepared composite material consists of zero-dimensional nanoparticles, one-dimensional nanorods, and two-dimensional nanosheets, exhibiting a multidimensional structure. This composite material demonstrates excellent catalytic activity and good stability for electrocatalytic hydrogen evolution, oxygen evolution, and the complete decomposition of water, showing great promise for application in water electrolysis hydrogen production technology.

Description

Technical Field

[0001] This invention relates to the preparation and application of a multidimensional S-doped MnCo2O4 nanorod / N-doped carbon nanosheet composite material, and more particularly to a multidimensional, high specific surface area, and highly hydrophilic S-doped MnCo2O4 nanorod / N-doped carbon nanosheet multidimensional composite material prepared using N-doped carbon aerogel prepared from biomass chitosan as a substrate. It is mainly used for electrocatalytic hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and water electrolysis reaction in alkaline media. Background Technology

[0002] In recent years, with the increasing demand for clean energy and the growing environmental pollution, developing clean energy to replace non-renewable energy sources such as coal and oil has become a global research hotspot. Water electrolysis for hydrogen production, using water as a raw material, is a clean, sustainable, and large-scale green method for hydrogen production, powered by solar, tidal, and wind energy. Water electrolysis includes the hydrogen evolution reaction (HER) at the cathode and the oxygen evolution reaction (OER) at the anode. During water electrolysis, the high overpotential and slow kinetic rates of HER and OER limit the improvement of electrolysis efficiency, hindering the large-scale application of this technology. To date, the noble metal Pt / C remains the most active commercial catalyst for HER, while RuO2 / IrO2 is the most active commercial catalyst for OER. However, noble metal catalysts are scarce, expensive, and have poor stability under alkaline conditions, severely hindering their large-scale commercial application.

[0003] In recent years, the development of low-cost, high-efficiency, and stable non-precious metal catalysts has been of great significance. Among various types of electrocatalysts, including transition metal oxides, hydroxides, phosphides, sulfides, nitrides, and alloys, transition metal oxides have attracted widespread attention due to their low cost, abundant resources, and high OER catalytic activity in alkaline electrolytes. Spinel oxides, in particular, have become a research hotspot due to their advantages such as multifunctionality, diverse structures, low toxicity, low cost, and tunable metal ion valence states. MnCo₂O₄ (manganese cobalt oxide) exhibits high OER catalytic activity; however, its poor conductivity limits its catalytic performance.

[0004] Composites with carbon materials (graphene, carbon nanotubes, carbon aerogels) can effectively improve the electrical conductivity of MnCo₂O₄, thereby enhancing its electrocatalytic activity. Carbon aerogels possess a large surface area and good hydrophilic properties, and chitosan carbon aerogels can undergo in-situ N doping during formation. Composites of spinel oxide MnCo₂O₄ with chitosan carbon aerogels can effectively increase the specific surface area of ​​the composite material, improve its hydrophilicity, and thus enhance its electrocatalytic performance. Furthermore, the Co content in spinel oxides can be controlled by a small amount of S doping. 3+ / Co 2+ The ratio of active sites to reactants is optimized to improve the intrinsic activity of MnCo2O4. Therefore, a multi-component catalyst is constructed by combining MnCo2O4 with chitosan carbon aerogel, and a small amount of sulfur doping is used to adjust the ratio of different metal valence states. This achieves complementary and synergistic effects between different components, improving the catalyst's multifunctional and intrinsic activity. Furthermore, the hydrophilicity of the catalyst is crucial for enhancing its catalytic activity. Chitosan carbon aerogel exhibits good hydrophilicity due to its abundant hydroxyl and amino groups. Loading MnCo2O4 onto the surface of chitosan carbon aerogel gives the composite material good hydrophilic properties, which is beneficial for promoting the charge transfer rate between the electrolyte and the electrode, thus enhancing electrocatalytic activity. Moreover, the morphology of the catalyst also significantly affects its activity. Generally, multidimensional composite structures are more advantageous than single-dimensional materials. Therefore, a simple, effective, and controllable method is urgently needed to prepare multidimensional sulfur-doped MnCo2O4 nanorod / N-doped carbon nanosheet composite catalysts and apply them to the electrolysis of water for hydrogen evolution, oxygen evolution, and total water decomposition reactions. Summary of the Invention

[0005] The purpose of this invention is to provide a simple, effective, and controllable method for preparing multidimensional S-doped MnCo2O4 / N-doped carbon composite materials.

[0006] Another object of the present invention is to provide the application of the composite material in electrocatalytic HER, OER and water electrolysis.

[0007] I. Preparation of Multidimensional S-Doped MnCo2O4 Nanorods / N-Doped Carbon Nanosheets Composite Material (S-MnCo2O4-NR / NCNS)

[0008] The preparation of S-MnCo2O4-NR / NCNS according to the present invention includes the following process steps:

[0009] (1) Preparation of two-dimensional N-doped carbon nanosheets (NCNS): Chitosan powder was added to distilled water, and glacial acetic acid was added dropwise while stirring continuously to dissolve the chitosan. The solution was then transferred to a petri dish and frozen at -20 °C for 24 h, followed by freeze-drying in a freeze dryer to obtain a dry aerogel. The obtained dry aerogel was carbonized in a tube furnace at 700-900 °C (preferably 800 °C) for 2-6 h (preferably 4 h) under N2 atmosphere, with a heating rate of 5 °C / min, to obtain a chitosan carbon aerogel with a three-dimensional structure. The obtained carbon aerogel was mixed with KOH and thoroughly ground, and then treated in a tube furnace at 700-900 °C (preferably 800 °C) for 2-6 h (preferably 4 h) under N2 atmosphere, with a heating rate of 5 °C / min, to obtain two-dimensional N-doped carbon nanosheets. The mass-to-volume ratio of chitosan powder to glacial acetic acid is 2-3 g / mL; the mass ratio of dry aerogel to KOH is 1:1-1:3.

[0010] Chitosan contains abundant amino and oxygen elements, which can generate nitrogen-doped carbon materials during the carbonization process. The carbon materials contain abundant nitrogen- and oxygen-containing groups (hydroxyl and carbonyl groups), which can not only improve the hydrophilicity of the carbon materials, but also facilitate coordination with metal ions, so that the metal ions are uniformly dispersed on the prepared carbon materials.

[0011] (2) Preparation of multidimensional MnCo2O4 nanorods / N-doped carbon nanosheets (MnCo2O4-NR / NCNS): Manganese salt, cobalt salt and urea were completely dissolved in distilled water to form a solution. The resulting solution was transferred to a reaction vessel, and then NCNS prepared in step (1) was added to it. After hydrothermal reaction at 120 °C for 7-9 h, the product was centrifuged and washed. The solid product was then vacuum dried. The dried sample was heat-treated in a tube furnace at 300 °C for 2-6 h (preferably 4 h) under N2 atmosphere, with a heating rate of 2 °C / min. During this process, the abundant nitrogen- and oxygen-containing groups (hydroxyl and carbonyl groups) on the N-doped carbon nanosheets were coordinated with metal Mn and Co ions, so that the metal ions were uniformly dispersed on the carbon nanosheets. Urea acted as a precipitant to precipitate the metal ions to form the corresponding metal hydroxides, which were then converted into spinel-type MnCo2O4 under hydrothermal conditions, thus preparing the multidimensional MnCo2O4-NR / NCNS composite material. The molar ratio of manganese salt, cobalt salt, and urea is 1:2:3; the mass ratio of NCNS to manganese salt is 1:4-1:10. The manganese salt is one of MnCl2·4H2O, Mn(CH3COO)2, MnSO4, and Mn(NO3)2; the cobalt salt is one of Co(NO3)2·6H2O, CoCl2·6H2O, and Co(CH2COO)2·4H2O.

[0012] (3) Preparation of multidimensional S-doped MnCo2O4 nanorods / N-doped carbon nanosheets composite material (S-MnCo2O4-NR / NCNS): Sulfur powder and MnCo2O4-NR / NCNS were placed at the inlet and outlet of a tube furnace, respectively, in a N2 atmosphere, and heat-treated at 300 ℃ for 2-6 h (preferably 3 h), with a heating rate of 2 ℃ / min. During this process, sulfur powder sublimated to generate sulfur vapor, which reacted with MnCo2O4, resulting in a small amount of S being incorporated into MnCo2O4, generating S-doped MnCo2O4 nanorods, thereby obtaining the S-MnCo2O4-NR / NCNS composite material. The mass ratio of sulfur powder to MnCo2O4-NR / NCNS was 1:5-1:10.

[0013] II. Structure and Composition of Multidimensional S-MnCo2O4-NR / NCNS Composite Material

[0014] Figure 1 These are scanning electron microscope (SEM) and transmission electron microscope (TEM) images of the chitosan carbon aerogel and S-MnCo2O4-NR / NCNS composite material prepared in Example 1 of this invention. As shown in the figures, the prepared chitosan carbon aerogel exhibits a three-dimensional structure composed of stacked nanosheets, and the surface of the nanosheets is smooth. Figure 1 a). The final S-MnCo2O4-NR / NCNS composite material consists of one-dimensional S-MnCo2O4-NR nanorods and two-dimensional NCNS. Figure 1 b), where the one-dimensional S-MnCo2O4-NR nanorods are composed of zero-dimensional S-MnCo2O4 nanoparticles ( Figure 1 cd). Zero-dimensional S-MnCo2O4 nanoparticles have a diameter of 20-30 nm, while one-dimensional S-MnCo2O4-NR nanorods have a length of several micrometers and a diameter of about 100 nm. Figure 1 cd).

[0015] Figure 2 The following are XRD patterns of the catalysts prepared in Examples 1-4 of this invention: (a) Example 1; (b) Example 2; (c) Example 3; (d) Example 4. As shown in the figures, all four catalysts prepared contain spinel-type S-MnCo2O4. The diffraction peaks at 2θ of approximately 18.5, 30.5, 35.9, 43.7, 57.8, and 75.2° are attributed to the (111), (220), (311), (400), (511), and (533) crystal planes of spinel-type S-MnCo2O4, respectively (PDF No. 84-0428). Because the carbon peak is broad and has low intensity, it is masked by the sharp and strong diffraction peaks of S-MnCo2O4, so the presence of the carbon peak was not detected in the XRD patterns.

[0016] Figure 3 This is the Raman spectrum of the catalyst prepared in Example 1 of this invention, at a wavenumber of 1361 nm. -1 and 1595nm -1 The detection of D and G peaks at the point confirms the presence of carbon materials.

[0017] Figure 4 This is the N2 adsorption-desorption isotherm of the catalyst prepared in Example 1 of this invention. The isotherm shows that the obtained sample exhibits a type IV isotherm and an H1 hysteresis loop, indicating that the obtained catalyst has a rich pore structure and a large specific surface area. The specific surface area of ​​this sample is 181.20 m². 2 / g, pore volume is 0.39cm³ 3 / g.

[0018] Figure 5 This is a pore size distribution diagram of the catalyst prepared in Example 1 of the present invention. As can be seen from the figure, the obtained sample has a wide pore size distribution range, between 20-47 nm, and is mainly concentrated in the mesoporous range of 30-44 nm, which further proves that the catalyst has a rich mesoporous structure.

[0019] Figure 6 This is a contact angle test of the catalyst prepared in Example 1 of this invention. It can be seen that, thanks to the abundance of nitrogen- and oxygen-containing groups (hydroxyl and carbonyl groups) in the N-doped carbon nanosheets, which have strong hydrophilicity, the resulting composite material also has good hydrophilicity, with a contact angle of only 36°.

[0020] III. Electrocatalytic performance of multidimensional S-MnCo2O4-NR / NCNS composite materials

[0021] The composite material was used to fabricate working electrodes for electrocatalytic hydrogen evolution, oxygen evolution, and water electrolysis: A certain amount of the composite material was ultrasonically dispersed in ethanol, and an appropriate amount of 5% Nafion solution was added and mixed evenly to prepare a suspension. A certain amount of this suspension was drop-coated onto a glassy carbon electrode and allowed to air dry to prepare working electrodes for electrocatalytic hydrogen evolution and oxygen evolution; a certain amount of this suspension was also drop-coated onto treated nickel foam to prepare a working electrode for electrocatalytic water splitting. Electrochemical performance tests were conducted using a CHI760E electrochemical workstation.

[0022] Figure 7 The figure shows the LSV curve of the catalyst prepared in Example 1 of this invention catalyzing HER in 1.0 M KOH. As can be seen from the figure, the obtained catalyst achieves a current density of 10 mA / cm² when catalyzing HER in 1.0 M KOH. 2 The overpotential was 129 mV, demonstrating that the catalyst has excellent catalytic activity for HER.

[0023] Figure 8This is the LSV curve of the catalyst prepared in Example 1 of this invention catalyzing OER in 1.0 M KOH. As shown in the figure, the obtained catalyst achieves a current density of 10 mA / cm² when catalyzing OER in 1.0 M KOH. 2 The overpotential was 222 mV, which proves that the catalyst has excellent catalytic activity for OER.

[0024] Figure 9 The figure shows the LSV curve of the catalyst prepared in Example 1 of this invention for catalytic water electrolysis in 1.0 M KOH. As can be seen from the figure, the obtained catalyst achieves a current density of 10 mA / cm² during the total decomposition of water in 1.0 M KOH. 2 The decomposition voltage was 1.570 V, proving that the catalyst, as a bifunctional catalyst for HER and OER, has excellent catalytic activity for water electrolysis.

[0025] Figure 10 This is the voltage-time curve of the catalyst prepared in Example 1 of this invention for catalytic water electrolysis in 1.0 M KOH. As shown in the figure, the obtained catalyst at 10 mA / cm²... 2 After a 26-hour Vt stability test, the decomposition voltage increased by only 27 mV, demonstrating that the catalyst has good stability during the catalytic electrolysis of water.

[0026] The above test results indicate that in a 1.0 M KOH solution, at 10 mA / cm², 2 At the specified current density, the overpotential of this catalyst for HER can be as low as 129 mV, the overpotential for OER can be as low as 222 mV, and the decomposition voltage for water electrolysis can be as low as 1.570 V, and it also exhibits good cycle stability.

[0027] The reaction mechanism of this invention is as follows: Chitosan is used as both a nitrogen and carbon source to prepare carbon aerogel, which is then further activated and carbonized with KOH to transform the carbon aerogel into two-dimensional N-doped carbon nanosheets. Because chitosan contains abundant amino and oxygen elements, the prepared N-doped carbon nanosheets contain abundant nitrogen- and oxygen-containing groups (hydroxyl and carbonyl groups), which not only improves the hydrophilicity of the carbon material but also facilitates coordination with metal ions, resulting in uniform dispersion of metal ions on the prepared carbon material. In the preparation of the multidimensional MnCo2O4-NR / NCNS composite material, the abundant nitrogen- and oxygen-containing groups (hydroxyl and carbonyl groups) on the N-doped carbon nanosheets coordinate with metal Mn and Co ions, resulting in uniform dispersion of metal ions on the carbon nanosheets. Urea acts as a precipitant, causing the metal ions to precipitate and form corresponding metal hydroxides, which are then converted into spinel-type MnCo2O4 under hydrothermal conditions, thus producing the multidimensional MnCo2O4-NR / NCNS composite material.

[0028] During the vulcanization process of multidimensional MnCo2O4-NR / NCNS composite material with sulfur powder, the sulfur powder sublimates to generate sulfur vapor, which reacts with MnCo2O4, resulting in a small amount of S being incorporated into MnCo2O4, generating S-doped MnCo2O4, thereby producing multidimensional S-MnCo2O4-NR / NCNS composite material.

[0029] The composition, structure, and catalytic performance of a catalyst can be controlled by adjusting the mass ratio of carbon materials to metal ions, the mass ratio of sulfur powder to MnCo2O4-NR / NCNS, as well as the hydrothermal reaction temperature, the heat treatment temperature in a N2 atmosphere, and the reaction time. For example, increasing the proportion of metal ions can increase the content of S-MnCo2O4 in the catalyst; increasing the hydrothermal reaction temperature and extending the hydrothermal reaction time can increase the particle size of S-MnCo2O4. Increasing the content of carbon nanosheets can increase the specific surface area of ​​the composite material, thereby creating a more abundant pore structure in the final catalyst, which is beneficial to improving the mass transfer and charge transport kinetics of the catalyst, thus improving its catalytic activity. Optimizing the amount of sulfur powder can optimize the sulfur doping amount in S-MnCo2O4, thereby optimizing the catalyst activity.

[0030] Compared with the prior art, the present invention has the following advantages:

[0031] 1. Carbon materials are prepared using natural high-molecular-weight chitosan as a raw material. Taking advantage of its abundant amino and oxygen elements, nitrogen-doped carbon materials can be obtained in situ and uniformly without the need for an external nitrogen source. Furthermore, the prepared carbon materials contain a large number of nitrogen- and oxygen-containing groups (hydroxyl and carbonyl groups). These groups can coordinate with metal Mn and Co ions, allowing the metal ions to be uniformly dispersed on the carbon nanosheets and chelating them, resulting in a uniform distribution of elements in the final catalyst.

[0032] 2. By doping with sulfur, the electron density of metal ions and the strength of chemical bonds between metal and oxygen, and between metal and sulfur, are adjusted, thereby optimizing the adsorption and activation performance of active sites on reactant molecules and the formation activity of reactive intermediates, thus improving the electrocatalytic activity of the catalyst.

[0033] 3. N-doped carbon nanosheets contain a large number of nitrogen- and oxygen-containing groups (hydroxyl and carbonyl groups), thus exhibiting excellent hydrophilicity and significantly improving the wettability of the catalyst by the electrolyte solution. N-doped carbon nanosheets also possess good electrical conductivity, which can enhance the conductivity of the composite catalyst. Furthermore, N-doped carbon nanosheets have a high specific surface area and abundant pore structure, especially mesoporous structures, which are beneficial for improving the rates of mass transfer and charge transport, as well as reaction kinetics, during the catalytic reaction, while exposing more active sites. These properties greatly promote the improvement of catalyst performance.

[0034] 4. The composite material consists of zero-dimensional S-MnCo2O4 nanoparticles, one-dimensional S-MnCo2O4 nanorods, and two-dimensional N-doped carbon nanosheets, exhibiting a multi-dimensional composite structure. Compared with materials with single-dimensional structures, this multi-dimensional composite structure has a strong synergistic effect, which can greatly improve the activity of the catalyst.

[0035] 5. The interfacial effect between N-doped carbon nanosheets and S-MnCo2O4 nanorods can greatly promote charge transport and improve electrocatalytic performance.

[0036] 6. Activity tests show that the composite material prepared in this invention has excellent electrocatalytic activity for hydrogen evolution, oxygen evolution and water electrolysis reactions, and has good stability in alkaline media, showing great application prospects. Attached Figure Description

[0037] Figure 1 These are SEM and TEM images of the catalyst prepared in Example 1 of this invention.

[0038] Figure 2 The following are XRD patterns of the catalysts prepared in Examples 1-4 of this invention: (a) Example 1; (b) Example 2; (c) Example 3; (d) Example 4;

[0039] Figure 3 This is the Raman diagram of the catalyst prepared in Example 1 of this invention.

[0040] Figure 4 This is the N2 adsorption-desorption isotherm of the catalyst prepared in Example 1 of this invention.

[0041] Figure 5 This is a pore size distribution diagram of the catalyst prepared in Example 1 of the present invention.

[0042] Figure 6 This refers to the contact angle measurement of the catalyst prepared in Example 1 of this invention.

[0043] Figure 7 This is the LSV curve of HER catalyzed by the catalyst prepared in Example 1 of this invention in 1.0M KOH.

[0044] Figure 8 This is the LSV curve of the catalyst prepared in Example 1 of this invention catalyzing OER in 1.0 M KOH.

[0045] Figure 9 This is the LSV curve of the catalyst prepared in Example 1 of this invention for catalytic electrolysis of water in 1.0 M KOH.

[0046] Figure 10This is the potential-time curve of the catalyst prepared in Example 1 of this invention catalyzing the electrolysis of water in 1.0 M KOH. Detailed Implementation

[0047] The present invention will now be described in more detail through specific embodiments.

[0048] Example 1

[0049] 1. Preparation of composite catalysts

[0050] (1) Preparation of two-dimensional NCNS: 1.0 g of chitosan powder was added to 40 mL of distilled water, and then 400 μL of glacial acetic acid was added dropwise while stirring continuously to dissolve the chitosan. The solution was then transferred to a petri dish and frozen at -20 °C for 24 h, and then freeze-dried in a freeze dryer to obtain a dry aerogel. In N2, the obtained dry aerogel was carbonized in a tube furnace at 800 °C for 4 h with a heating rate of 5 °C / min to obtain chitosan carbon aerogel. The obtained carbon aerogel was mixed with a certain amount of KOH (the mass ratio of carbon aerogel to KOH was 1:2) and ground thoroughly. Then, it was treated in a tube furnace at 800 °C for 4 h with a heating rate of 5 °C / min under N2 atmosphere to obtain two-dimensional N-doped carbon nanosheets NCNS.

[0051] (2) Preparation of multidimensional MnCo2O4-NR / NCNS: 0.792 g (4 mmol) MnCl2·4H2O, 1.903 g (8 mmol) CoCl2·6H2O and 0.721 g (12 mmol) urea were dissolved in 60 mL of distilled water and stirred until completely dissolved. The solution was then transferred to a 90 mL reactor. 0.1 g of the two-dimensional NCNS prepared above was added to the above solution. The mixture was hydrothermally reacted at 120 °C for 8 h. After centrifugation and washing, the solid product was vacuum dried at 80 °C for 24 h. The dried sample was then heat-treated in a tube furnace at 300 °C for 4 h under N2 atmosphere at a heating rate of 2 °C / min to obtain the multidimensional MnCo2O4 nanorod / N-doped carbon nanosheet composite material MnCo2O4-NR / NCNS. The molar ratio of manganese salt, cobalt salt and urea was 1:2:3; the mass ratio of NCNS to manganese salt was 1:8.

[0052] (3) Preparation of multidimensional S-MnCo2O4-NR / NCNS: Sulfur powder and a certain amount of the prepared MnCo2O4-NR / NCNS were placed in the inlet and outlet of a tube furnace, respectively, in N2, and heat-treated at 300 ℃ for 3 h with a heating rate of 2 ℃ / min to obtain S-doped MnCo2O4 nanorods / N-doped carbon nanosheets composite material S-MnCo2O4-NR / NCNS. The mass ratio of sulfur powder to MnCo2O4-NR / NCNS was 1:8.

[0053] The resulting composite catalyst consists of one-dimensional S-doped spinel MnCo2O4 nanorods (S-MnCo2O4-NR) and two-dimensional N-doped carbon nanosheets (NCNS). Figures 1-3 One-dimensional S-MnCo2O4 nanorods are composed of zero-dimensional S-MnCo2O4 nanoparticles. Figure 1 cd). The content of S-MnCo2O4 was 45.2%, and the content of S was 3.1%. The diameter of the nanoparticles was in the range of 20-30 nm, and the nanorods were several micrometers long with a diameter of about 100 nm. Figure 1 Cd). The composite catalyst has a rich pore structure ( Figures 4-5 Its specific surface area is 181.2 m². 2 / g, with a wide pore size distribution ranging from 20 to 47 nm, and a pore volume of 0.39 cm³. 3 / g. The composite catalyst exhibits good hydrophilicity, with a contact angle of 36° ( Figure 6 ).

[0054] 2. Catalytic performance test

[0055] Test Method: 5.0 mg of the prepared catalyst was weighed and added to a solution of 0.5 mL anhydrous ethanol and 10 μL Nafion (Dupont, 5 wt%). The mixture was sonicated for 30 min, and 5 μL of the suspension was coated onto a 3 mm glassy carbon electrode. Using the prepared glassy carbon electrode as the working electrode, a graphite electrode as the counter electrode, an Ag / AgCl electrode as the reference electrode, and 1.0 M KOH as the electrolyte, HER and OER tests were performed in a three-electrode system. For the water electrolysis performance test, a two-electrode system was used, with the prepared suspension dropped onto two 1 cm electrodes. 2 On the nickel foam, the catalyst loading was 1 mg / cm³. 2 The cathode and anode were fabricated and tested in a 1.0 M KOH solution. Stability testing was performed at a current density of 10 mA / cm². 2 The time-potential-time curve method. Stability is represented by the relationship between potential and time.

[0056] Test results: at a current density of 10 mA / cm² 2 At that time, the overpotential for catalytic HER was 129 mV ( Figure 7 The overpotential for catalytic OER is 222 mV. Figure 8 The decomposition voltage of catalytic water electrolysis is 1.570 V. Figure 9 The catalyst exhibits excellent stability at 10 mA / cm². 2After a 26-hour Vt stability test, its decomposition voltage increased by only 27mV. Figure 10 ).

[0057] Example 2

[0058] 1. Preparation of composite catalysts

[0059] (1) Preparation of two-dimensional NCNS: Same as in Example 1.

[0060] (2) Preparation of multidimensional MnCo2O4-NR / NCNS: 0.792 g (4 mmol) MnCl2·4H2O, 1.903 g (8 mmol) CoCl2·6H2O and 0.721 g (12 mmol) urea were dissolved in 60 mL of distilled water and stirred until completely dissolved. The solution was then transferred to a 90 mL reactor. 0.2 g of the two-dimensional NCNS prepared above was added to the above solution and hydrothermally reacted at 120 °C for 8 h. After centrifugation and washing, the solid product was vacuum dried at 80 °C for 24 h. The dried sample was then heat-treated in a tube furnace at 300 °C for 4 h under N2 atmosphere at a heating rate of 2 °C / min to obtain the multidimensional MnCo2O4 nanorod / N-doped carbon nanosheet composite material MnCo2O4-NR / NCNS. The molar ratio of manganese salt, cobalt salt and urea was 1:2:3; the mass ratio of NCNS to manganese salt was 1:4.

[0061] (3) Same as Example 1.

[0062] The resulting composite catalyst consists of one-dimensional S-doped spinel MnCo2O4 nanorods (S-MnCo2O4-NR) and two-dimensional N-doped carbon nanosheets (NCNS). Figure 2 The one-dimensional S-MnCo₂O₄ nanorods are composed of zero-dimensional S-MnCo₂O₄ nanoparticles. The S-MnCo₂O₄ content is 34.8%, and the S content is 3.5%. The nanoparticle diameter is in the range of 20-30 nm, while the nanorods are several micrometers long and approximately 100 nm in diameter. The composite catalyst possesses a rich porous structure and a specific surface area of ​​190.1 m². 2 / g, with a wide pore size distribution ranging from 18 to 42 nm, and a pore volume of 0.41 cm³. 3 / g. The composite catalyst exhibits good hydrophilicity with a contact angle of 32°.

[0063] (3) Same as Example 1.

[0064] 2. Catalytic performance test

[0065] Test method: Same as Example 1.

[0066] Test results: at a current density of 10 mA / cm² 2 At this time, the overpotential for HER catalysis was 185 mV, the overpotential for OER catalysis was 292 mV, and the decomposition voltage for water electrolysis was 1.580 V. The catalyst exhibits excellent stability at 10 mA / cm². 2 After a 26-hour Vt stability test, its decomposition voltage increased by only 23mV.

[0067] Example 3

[0068] 1. Preparation of composite catalysts

[0069] (1) Preparation of two-dimensional NCNS: Same as in Example 1.

[0070] (2) Preparation of multidimensional MnCo2O4-NR / NCNS: Same as in Example 1.

[0071] (3) Except that the mass ratio of sulfur powder to MnCo2O4-NR / NCNS is 1:10, the rest is the same as in Example 1.

[0072] The resulting composite catalyst consists of one-dimensional S-doped spinel MnCo2O4 nanorods (S-MnCo2O4-NR) and two-dimensional N-doped carbon nanosheets (NCNS). Figure 2 The one-dimensional S-MnCo₂O₄ nanorods are composed of zero-dimensional S-MnCo₂O₄ nanoparticles. The S-MnCo₂O₄ content is 38.9%, and the S content is 2.5%. The nanoparticle diameter is in the range of 20-30 nm, while the nanorods are several micrometers long and approximately 100 nm in diameter. The composite catalyst possesses a rich porous structure and a specific surface area of ​​185.5 m². 2 / g, with a wide pore size distribution ranging from 22 to 44 nm, and a pore volume of 0.38 cm³. 3 / g. The composite catalyst exhibits good hydrophilicity with a contact angle of 38°.

[0073] 2. Catalytic performance test

[0074] Test method: Same as Example 1.

[0075] Test results: at a current density of 10 mA / cm² 2 At this time, the overpotential for HER catalysis was 145 mV, the overpotential for OER catalysis was 268 mV, and the decomposition voltage for water electrolysis was 1.573 V. The catalyst exhibits excellent stability at 10 mA / cm². 2 After a 26-hour Vt stability test, its decomposition voltage increased by only 25mV.

[0076] Example 4

[0077] 1. Preparation of composite catalysts

[0078] (1) Preparation of two-dimensional NCNS: Same as in Example 1.

[0079] (2) Preparation of multidimensional MnCo2O4-NR / NCNS: Except that the sample was heat-treated at 300 °C for 6 h in N2 atmosphere, the rest was the same as in Example 1.

[0080] (3) Same as Example 1.

[0081] The resulting composite catalyst consists of one-dimensional S-doped spinel MnCo2O4 nanorods (S-MnCo2O4-NR) and two-dimensional N-doped carbon nanosheets (NCNS). Figure 2 The one-dimensional S-MnCo₂O₄ nanorods are composed of zero-dimensional S-MnCo₂O₄ nanoparticles. The S-MnCo₂O₄ content is 46.8%, and the S content is 4.2%. The nanoparticle diameter is in the range of 25-30 nm, while the nanorods are several micrometers long and approximately 100 nm in diameter. The composite catalyst possesses a rich porous structure and a specific surface area of ​​178.0 m². 2 / g, with a wide pore size distribution ranging from 30 to 45 nm, and a pore volume of 0.36 cm³. 3 / g. The composite catalyst exhibits good hydrophilicity with a contact angle of 45°.

[0082] 2. Catalytic performance test

[0083] Test method: Same as Example 1.

[0084] Test results: at a current density of 10 mA / cm² 2 At this time, the overpotential for HER catalysis was 164 mV, the overpotential for OER catalysis was 285 mV, and the decomposition voltage for water electrolysis was 1.575 V. The catalyst exhibits excellent stability at 10 mA / cm². 2 After a 26-hour Vt stability test, its decomposition voltage increased by only 32 mV.

Claims

1. A method for preparing a multidimensional S-doped manganese cobalt oxide nanorod / N-doped carbon nanosheet composite material, comprising the following process steps: (1) Preparation of two-dimensional N-doped carbon nanosheets: Chitosan powder was added to distilled water, and then glacial acetic acid was added dropwise and stirred continuously to dissolve the chitosan. The resulting solution was first frozen at -20 °C for 24 h, and then freeze-dried in a freeze dryer to obtain dry aerogel. Under N2 atmosphere, the obtained dry aerogel was carbonized in a tube furnace at 700-900 °C for 2-6 h to obtain chitosan carbon aerogel. The obtained chitosan carbon aerogel was mixed with KOH and ground thoroughly. Then, under N2 atmosphere, it was treated in a tube furnace at 700-900 °C for 2-6 h to obtain two-dimensional N-doped carbon nanosheets, named NCNS. (2) Preparation of multidimensional MnCo2O4 nanorod / N-doped carbon nanosheet composite material: Manganese salt, cobalt salt and urea were completely dissolved in distilled water to form a solution. The resulting solution was transferred to a reaction vessel, and then NCNS prepared in step (1) was added to it. After hydrothermal reaction at 120℃ for 7-9 h, the product was centrifuged and washed. The solid product was vacuum dried. The dried sample was heat-treated at 300℃ for 2-6 h under N2 atmosphere with a heating rate of 2℃ / min to obtain N-doped carbon nanosheet supported MnCo2O4 nanorod composite material, named MnCo2O4-NR / NCNS; the molar ratio of manganese salt, cobalt salt and urea was 1:2:3; the mass ratio of NCNS to manganese salt was 1:4-1:

10. (3) Preparation of multidimensional S-doped MnCo2O4 nanorods / N-doped carbon nanosheets composite material: Sulfur powder and MnCo2O4-NR / NCNS were placed at the inlet and outlet of a tube furnace, respectively, and heat-treated at 300℃ for 2-6h in N2 atmosphere with a heating rate of 2℃ / min to prepare multidimensional S-doped MnCo2O4 nanorods / N-doped carbon nanosheets composite material, named S-MnCo2O4-NR / NCNS; the mass ratio of sulfur powder to MnCo2O4-NR / NCNS was 1:5-1:

10.

2. The method for preparing the multidimensional S-doped manganese cobalt oxide nanorod / N-doped carbon nanosheet composite material as described in claim 1, characterized in that: In step (1), the mass-to-volume ratio of chitosan powder to glacial acetic acid is 2-3 g / mL.

3. The method for preparing the multidimensional S-doped manganese cobalt oxide nanorod / N-doped carbon nanosheet composite material as described in claim 1, characterized in that: In step (1), the mass ratio of chitosan carbon aerogel to KOH is 1:1-1:

3.

4. The method for preparing the multidimensional S-doped manganese cobalt oxide nanorod / N-doped carbon nanosheet composite material as described in claim 1, characterized in that: In step (2), the manganese salt is one of MnCl2·4H2O, Mn(CH3COO)2, MnSO4, and Mn(NO3)2; the cobalt salt is one of Co(NO3)2·6H2O, CoCl2·6H2O, and Co(CH2COO)2·4H2O.

5. The method for preparing the multidimensional S-doped manganese cobalt oxide nanorod / N-doped carbon nanosheet composite material as described in claim 1, characterized in that: The prepared composite material consists of one-dimensional S-MnCo2O4-NR and two-dimensional NCNS, wherein the one-dimensional S-MnCo2O4-NR is composed of zero-dimensional S-MnCo2O4 nanoparticles.

6. The method for preparing the multidimensional S-doped manganese cobalt oxide nanorod / N-doped carbon nanosheet composite material as described in claim 1, characterized in that: The prepared composite material contains 30-60% S-MnCo2O4 and 1%-5% S; the specific surface area of ​​the composite material is 172-194 m². 2 / g, pore volume is 0.35-0.43cm³ 3 / g; contact angle is 30-52°.

7. The application of the multidimensional S-doped manganese cobalt oxide nanorod / N-doped carbon nanosheet composite material prepared by the method described in claim 1 in the hydrogen evolution reaction of water electrolysis.

8. The application of the multidimensional S-doped manganese cobalt oxide nanorod / N-doped carbon nanosheet composite material prepared by the method described in claim 1 in the oxygen evolution reaction of water electrolysis.

9. The application of the multidimensional S-doped manganese cobalt oxide nanorod / N-doped carbon nanosheet composite material prepared by the method described in claim 1 in the total water electrolysis reaction.

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