Transition metal nanoparticle embedded biomass-derived nitrogen-doped carbon electrocatalyst as well as preparation method and application thereof

Abstract

The invention discloses a transition metal nanoparticle embedded biomass-derived nitrogen-doped carbon electrocatalyst as well as a preparation method and application thereof, and belongs to the technical field of H2O2 preparation. The problems that a transition metal-carbon material catalyst is low in H2O2 selectivity, complex in preparation process and not environmentally friendly are solved. The preparation method of the electrocatalyst comprises the following steps: carrying out a hydrothermal reaction on a biomass fiber material and concentrated alkali liquor, then carrying out a hydrothermal reaction on obtained biomass cellulose, transition metal salt and an organic ligand to obtain a metal-loaded nitrogen-containing biomass carbon material, and carrying out heat treatment on the biomass carbon material to obtain the electrocatalyst. The electrocatalyst is used as a cathode to electrocatalyze two-electron oxygen reduction to synthesize H2O2. According to the invention, a nitrogen source easy to pyrolyze and oxidized fibers are coordinated and combined through hydro-thermal synthesis, and holes are etched and formed in the catalyst during high-temperature pyrolysis, so that the mesoporous content of the catalyst is increased; the catalyst has good ability of two-electron oxygen reduction electrosynthesis of H2O2, and the H2O2 selectivity and yield are high.

Description

Technical Field

[0001] This invention belongs to the field of H2O2 preparation technology, specifically relating to a transition metal nanoparticle embedded in biomass-derived nitrogen-doped carbon electrocatalyst, its preparation method, and its application. Background Technology

[0002] H2O2, a common green oxidant, has wide applications in aerospace, medical, and environmental fields. Currently, H2O2 production relies on the traditional anthraquinone process, which suffers from high energy consumption and complex processes, and is heavily dependent on fossil fuels. Electrocatalytic two-electron oxygen reduction (2e-ORR) can directly convert oxygen into H2O2. This process is mild, environmentally friendly, and has low production costs, while also avoiding transportation and storage difficulties, making it a potential alternative to the anthraquinone method for H2O2 production.

[0003] Currently, while noble metal catalysts (Pt-Hg, Pt-Au, etc.) have achieved good performance in the electrocatalytic two-electron oxygen reduction reaction, their high cost and scarcity limit their large-scale application. Research on introducing transition metals (such as iron, cobalt, nickel, and manganese) into carbon-based materials has received widespread attention, as transition metal-carbon materials hold promise as a replacement for noble metal-based catalysts. However, current transition metal-carbon catalysts exhibit low selectivity for the two-electron oxygen reduction to H2O2. During catalysis, oxygen dissociates and adsorbs at the metal active sites, completely breaking the O2O2 bond and reducing oxygen to water. Therefore, developing simple and environmentally friendly preparation processes to obtain transition metal-carbon materials with high H2O2 selectivity remains a significant challenge. Summary of the Invention

[0004] To address the problems of low selectivity, complex preparation process, and environmental unfriendliness of existing transition metal-carbon catalysts for H2O2, this invention provides a method for preparing and applying a transition metal nanoparticle-embedded biomass-derived nitrogen-doped carbon catalyst.

[0005] The technical solution of the present invention is as follows: One objective of this invention is to provide a method for preparing a transition metal nanoparticle-embedded biomass-derived nitrogen-doped carbon electrocatalyst, the method comprising: (1) Extraction of biomass cellulose: The dried and pulverized biomass fiber material is mixed with concentrated alkaline solution, and after hydrothermal reaction, the product is filtered, washed and vacuum dried to obtain biomass cellulose. (2) Preparation of nitrogen-containing biomass carbon materials loaded with metals: Biomass cellulose is pulverized and added to an organic solvent to form a cellulose dispersion. Organic ligands and transition metal salts are added to the cellulose dispersion in sequence to obtain a mixed dispersion. The mixed dispersion is subjected to hydrothermal reaction, and the product is filtered, washed, and vacuum dried to obtain a nitrogen-containing biomass carbon material loaded with metal. (3) Catalyst preparation: Nitrogen-containing biomass carbon materials loaded with metals were heat-treated under a nitrogen atmosphere to obtain transition metal nanoparticles embedded in biomass-derived nitrogen-doped carbon electrocatalysts.

[0006] Further specifying, (1) the biomass fiber material is at least one of corn stalks, wheat stalks, coconut shells, peanut shells, and rice stalks.

[0007] Further specify that (1) the concentrated alkaline solution is at least one of potassium hydroxide solution and sodium hydroxide solution, and the concentration of the alkaline solution is 3-5 mol / L.

[0008] Further, in (1), the hydrothermal reaction temperature is 120~200℃ and the time is 6~16h.

[0009] Further specifying, in (2), the mass ratio of biomass cellulose to transition metal salt is (0.5:1) ~ (0.05-0.25).

[0010] Further specifying, (2) the transition metal salt is at least one of cobalt chloride, ferric chloride or nickel chloride hexahydrate.

[0011] Further specifying, (2) the organic ligand is at least one of dicyandiamide, urea and melamine.

[0012] Further specifying, in (2), the molar ratio of transition metal salt to organic ligand is 1:(1~20).

[0013] Furthermore, in (2), the molar ratio of transition metal salt to organic ligand is 1:(1~10).

[0014] Furthermore, in (2), the molar ratio of transition metal salt to organic ligand is 1:(1~5).

[0015] Further, the concentration of organic ligands in the mixed dispersion of (2) is 0.1 mol / L to 0.4 mol / L.

[0016] Furthermore, the concentration of organic ligands in the mixed dispersion of (2) is 0.2 mol / L to 0.4 mol / L.

[0017] Furthermore, the concentration of organic ligands in the mixed dispersion of (2) is 0.2 mol / L to 0.3 mol / L.

[0018] Further specifying, in (2), the organic solvent is anhydrous methanol or anhydrous ethanol.

[0019] Further, in (2), the hydrothermal reaction temperature is 80~140℃ and the time is 8~14h.

[0020] Further specifying, the filtration and washing process in (1) and (2) is as follows: filtration is performed under a vacuum of 0.06~0.09MPa, followed by washing with deionized water 2-3 times, and then washing with anhydrous methanol or anhydrous ethanol 2-3 times.

[0021] Further specifying, the vacuum drying parameters in (1) and (2) are: drying temperature of 60~80℃ and time of 8~12h.

[0022] Further specified, (3) the heat treatment temperature is 600~900℃ and the time is 2~4h.

[0023] The second objective of this invention is to provide a transition metal nanoparticle embedded in a biomass-derived nitrogen-doped carbon electrocatalyst prepared by the above method.

[0024] The third objective of this invention is to provide an application of the above-mentioned transition metal nanoparticles embedded in a biomass-derived nitrogen-doped carbon electrocatalyst as a cathode in the electrocatalytic two-electron oxygen reduction synthesis of H2O2.

[0025] The beneficial effects of this invention are as follows: The electrocatalyst of this invention embeds transition metal nanoparticles into biomass-derived nitrogen-doped carbon for highly selective two-electron ORR electrosynthesis of H2O2. Compared with the prior art, this invention also has the following advantages: (1) The biomass cellulose obtained in step (1) of this invention is rod-shaped oxidized fiber. Through hydrothermal synthesis, easily pyrolytic nitrogen sources (urea, melamine, dicyandiamide) are fully coordinated and combined with the oxidized fiber. The oxidized fiber is also coordinated with carbon and metal at the same time, increasing the number of coordination sites. This allows for the etching and formation of pores on the catalyst during nitrogen atmosphere heat treatment, and the number of pores increases. These pores serve as catalytic sites, which is equivalent to greatly increasing the mesopore content of the catalyst. As a result, the catalyst has a good ability to electrosynthesize H2O2 by two-electron oxygen reduction, with an H2O2 selectivity of over 93%. The yield of H2O2 by large-scale electrosynthesis in the flow cell can reach up to 9.84 mol g. cat -1 h -1 .

[0026] (2) In step (2) of the present invention, the order of adding raw materials should be: first add organic ligands, then add transition metal salts. Nitrogen atoms first occupy the defect sites of biomass fiber carriers to form N-rich carriers, and then the added metal ions bind to the N-rich sites through coordination. However, if transition metal salts are added first, the metals first nucleate to form some metal-oxygen bonds, and the nitrogen source is difficult to completely replace O after coordination, forming mixed coordination sites and reducing the overall catalytic activity. Attached Figure Description

[0027] Figure 1 X-ray diffraction pattern of the Ni-NC electrocatalyst prepared in Example 1; Figure 2 The image shows a scanning electron microscope (SEM) image of the Ni-NC electrocatalyst prepared in Example 1. Figure 3 Linear sweep voltammetry (LSV) curves of the Ni-NC electrocatalyst prepared in Example 1 were obtained using a rotating ring disk electrode; Figure 4 The H2O2 selectivity and number of electrons transferred for the Ni-NC electrocatalyst prepared in Example 1 in 0.1M KOH solution; Figure 5 The results of cyclic voltammetry (CV) stability tests on the Ni-NC electrocatalyst prepared in Example 1 in 0.1 M KOH solution are shown. Figure 6 This is a diagram of the flow electrolysis cell apparatus for the Ni-NC electrocatalyst prepared in Example 1; Figure 7 The LSV polarization curve of the Ni-NC electrocatalyst prepared in Example 1 was obtained by a flow electrolysis cell in 1M KOH solution; Figure 8 The yield of H2O2 and the Faraday efficiency of the Ni-NC electrocatalyst prepared in Example 1 were determined in a flow electrolysis cell at different current densities in 1M KOH solution. Figure 9 The effect of the Ni-NC electrocatalyst prepared in Example 1 on the degradation of Rhodamine B dye in 1M KOH solution using a flowing electrolytic cell is shown in the figure. Figure 10 Linear sweep voltammetry (LSV) curves were obtained using a rotating ring disk electrode for the Ni-NC electrocatalyst prepared in Example 2. Figure 11 The H2O2 selectivity and number of transferred electrons of the Ni-NC electrocatalyst prepared in Example 2 in 0.1M KOH solution; Figure 12 Linear sweep voltammetry (LSV) curves of the Ni-NC-2 electrocatalyst prepared for Comparative Example 1 were obtained using a rotating ring disk electrode; Figure 13The H2O2 selectivity and number of transferred electrons of the Ni-NC-2 electrocatalyst prepared in Comparative Example 1 in 0.1M KOH solution. Detailed Implementation

[0028] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0029] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0030] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0031] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0032] Example 1 (1) Extraction of biomass cellulose: Dissolve 59g of potassium hydroxide in 350mL of deionized water to obtain a potassium hydroxide solution. Place 10g of dried and pulverized coconut shell shreds into a 500mL hydrothermal reactor. Pour the potassium hydroxide solution into the hydrothermal reactor. The mixture is hydrothermally reacted at 180℃ for 12h. The product is filtered under a vacuum of 0.09MPa. It is first washed 2-3 times with deionized water, and then washed 2-3 times with anhydrous methanol. The solid material obtained by filtration is then vacuum dried at 80℃ for 10h to obtain biomass cellulose. (2) Preparation of nitrogen-containing biomass carbon materials loaded with metals: 1 g of biomass cellulose was added to 60 mL of methanol to obtain a cellulose dispersion. 0.375 g of melamine and 0.15 g of nickel chloride hexahydrate were added to the cellulose dispersion to obtain a mixed dispersion. The mixed dispersion was transferred to a 100 mL hydrothermal reactor and hydrothermally reacted at 120 °C for 12 h. After the reaction was completed, the mixture was cooled to room temperature and filtered under a vacuum of 0.09 MPa. The product was washed 2-3 times with deionized water and then 2-3 times with anhydrous methanol. The solid obtained by filtration was then vacuum dried at 80 °C for 12 h to obtain a nickel-loaded nitrogen-containing biomass carbon material. (3) Catalyst preparation: Nitrogen-containing biomass carbon material loaded with nickel was calcined at 900℃ for 2 hours under a nitrogen atmosphere to obtain a nitrogen-doped carbon electrocatalyst with nickel nanoparticles embedded in biomass, denoted as Ni-NC electrocatalyst.

[0033] The X-ray diffraction (XRD) pattern of the Ni-NC electrocatalyst obtained in this embodiment is as follows: Figure 1 As shown, in Figure 1 As can be seen, the transition metal nickel exists in its elemental form, and its diffraction peaks correspond perfectly to those on the nickel PDF card.

[0034] The SEM image of the Ni-NC electrocatalyst obtained in Example 1 is as follows: Figure 2 As shown, the catalyst retains the rod-like structure of cellulose and has nickel nanoparticles embedded on its surface, which is beneficial for the nickel sites to combine with oxygen to carry out the 2e-ORR reaction.

[0035] The electrochemical performance of the Ni-NC electrocatalyst was tested using the following method: Preparation of the electrochemical working electrode: 5 mg of Ni-NC electrocatalyst, 600 µL of ethanol, and 50 µL of 0.5% naphthol were weighed and mixed, then sonicated for 30 min to prepare a uniform dispersion. 8 µL of this dispersion was then uniformly coated onto a glassy carbon electrode to obtain a Ni-NC electrocatalyst with a concentration of 0.1 mg / cm³. -2 The load capacity and the area of ​​the rotating ring electrode are 0.2475 cm². -2 The 2e-ORR performance of the catalyst was evaluated using a rotating ring-disk electrode in an O2-saturated 0.1M KOH solution via an electrochemical workstation (CHI760E, Shanghai Chenhua Instrument Co., Ltd.).

[0036] Figure 3 The disk-to-ring currents of the Ni-NC electrocatalyst are shown, with the disk current reaching 0.74 mA and the ring current reaching 0.2 mA.

[0037] Figure 4 Based on Figure 3 The H2O2 selectivity and the number of transferred electrons were calculated from the disk-ring current of the catalyst. The H2O2 selectivity reached 93%, and the number of transferred electrons was close to 2.1.

[0038] Figure 5 The stability of the Ni-NC electrocatalyst was evaluated by performing 5000 cycles of cyclic voltammetry (CV) in 0.1 M KOH solution. The results are as follows: Figure 5 As shown, the current density of the Ni-NC electrocatalyst decreased by only 0.2 mA cm⁻¹ compared to the initial stage. -2 This indicates that the Ni-NC electrocatalyst maintains good stability.

[0039] The electrocatalytic yield of H2O2, the Faradaic efficiency (FE), and the stability of the catalyst were tested using a three-electrode flow electrolysis cell apparatus. The flow electrolysis cell apparatus is as follows: Figure 6 As shown: Figure 7 LSV testing of the Ni-NC electrocatalyst in 1 M KOH was performed to determine the current range for subsequent hydrogen peroxide yield determination. It can be seen that the highest current density reached 150 mA cm⁻¹. -2 .

[0040] Figure 8 To investigate the yield and Faradaic efficiency of H2O2 using a Ni-NC electrocatalyst at different current densities in the range of 40–150 mA cm⁻¹ -2 The Faraday efficiency is greater than 85% at all current densities, and is even greater at 150 mA cm⁻¹. -2 The highest yield of H2O2 was achieved at the lowest current density, reaching 9.84 mol g. cat -1 h -1 .

[0041] Figure 9 For Ni-NC electrocatalyst at 80 mA cm -2 The catalytic degradation effect of Rhodamine B dye under current density for 30 min was investigated. The figure shows that the Ni-NC electrocatalyst can decolorize Rhodamine B dye at a concentration of 250 mg / L, and the degradation rate of Rhodamine B dye is 99.6%. Example 2 The difference between this embodiment and embodiment 1 is that: (2) 0.75g of melamine, 0.1g of nickel chloride hexahydrate, and the molar ratio of transition metal salt to organic ligand is 1:7.5. The remaining process steps and parameter settings are the same as in embodiment 1.

[0042] Comparative Example 1 The difference from Example 1 is that (2) the order of adding ligands and transition metal salts was changed. Nickel chloride hexahydrate was added first, followed by melamine. The remaining process steps and parameter settings were the same as in Example 1. The resulting electrocatalyst was denoted as Ni-NC-2 electrocatalyst.

[0043] In Example 1, while the disk current reaches 0.74 mA, the ring current also reaches 0.2 mA, and through Figure 12 As can be seen from the LSV curves, in Comparative Example 1, the disk current is 1.2 mA, while the ring current is almost zero.

[0044] In Example 1, the selectivity of hydrogen peroxide was above 85% over a wide potential range, and the number of transferred electrons was closer to 2. Figure 13The H2O2 selectivity and electron transfer graphs show that in Comparative Example 1, the hydrogen peroxide selectivity is below 10% over a wide electrical range, and the number of transferred electrons is closer to 4 electrons.

[0045] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a transition metal nanoparticle-embedded biomass-derived nitrogen-doped carbon electrocatalyst, characterized in that, The preparation method includes: (1) Extraction of biomass cellulose: The dried and pulverized biomass fiber material is mixed with concentrated alkaline solution, and after hydrothermal reaction, the product is filtered, washed and vacuum dried to obtain biomass cellulose. (2) Preparation of nitrogen-containing biomass carbon materials loaded with metals: Biomass cellulose is pulverized and added to an organic solvent to form a cellulose dispersion. Organic ligands and transition metal salts are added to the cellulose dispersion in sequence to obtain a mixed dispersion. The mixed dispersion is subjected to hydrothermal reaction, and the product is filtered, washed, and vacuum dried to obtain a nitrogen-containing biomass carbon material loaded with metal. (3) Catalyst preparation: Nitrogen-containing biomass carbon materials loaded with metals were heat-treated under a nitrogen atmosphere to obtain transition metal nanoparticles embedded in biomass-derived nitrogen-doped carbon electrocatalysts.

2. The preparation method according to claim 1, characterized in that, (1) The biomass fiber material is at least one of corn stalks, wheat stalks, coconut shells, peanut shells, and rice stalks. The concentrated alkali solution is potassium hydroxide solution and / or sodium hydroxide solution, and the concentration of the alkali solution is 3-5 mol / L.

3. The preparation method according to claim 1, characterized in that, (1) The hydrothermal reaction temperature is 120~200 ℃ and the time is 6~16 h.

4. The preparation method according to claim 1, characterized in that, (2) The transition metal salt is at least one of cobalt chloride, ferric chloride or nickel chloride hexahydrate, and the organic ligand is at least one of dicyandiamide, urea or melamine.

5. The preparation method according to claim 1, characterized in that, (2) The molar ratio of transition metal salt to organic ligand is 1:(1~20), the concentration of organic ligand in the mixed dispersion is 0.1mol / L~0.4mol / L, and the mass ratio of biomass cellulose to transition metal salt is (0.5:1)~(0.05-0.25).

6. The preparation method according to claim 1, characterized in that, (2) The organic solvent is anhydrous methanol or anhydrous ethanol.

7. The preparation method according to claim 1, characterized in that, (2) The hydrothermal reaction temperature is 80~140℃ and the time is 8~14 h.

8. The preparation method according to claim 1, characterized in that, (3) The heat treatment temperature is 600~900℃ and the time is 2~4 h.

9. A transition metal nanoparticle-embedded biomass-derived nitrogen-doped carbon electrocatalyst prepared by the preparation method according to any one of claims 1 to 8.

10. A transition metal nanoparticle as described in claim 9, embedded in a biomass-derived nitrogen-doped carbon electrocatalyst as a cathode, for electrocatalyzing the two-electron oxygen reduction reaction to synthesize H2O2.

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