Nano-defect porous carbon material with high bonding BS content and preparation method and application thereof

Abstract

The present invention discloses a nano-defect porous carbon material (BS-C) with a high B-S (bonding) content, a preparation method, and an application thereof. The B content in the material can reach 1.5at%-6at%, and the S content can reach 0.5at%-2at%. The material has micropores, mesopores, and macropores distributed in it, and a specific surface area of 700m 2 g ‑1 ‑1300m 2 g ‑1 . Sodium lignin sulfonate is used as a carbon source and boric acid as a boron source. After pretreatment, a precursor is prepared and annealed at high temperature to prepare a nano-defective porous carbon material with a high B-S content. The high-temperature annealing process can form special chemical bonds between B and C and S. During annealing, boric acid can not only act as a boron source to provide bonding B atoms to the carbon material, but also promote the formation of porous structures and nano-defect structures of the material. The material can efficiently electrocatalyze the two-electron oxygen reduction reaction.

Description

Technical field:

[0001] The present invention relates to a preparation method and application of a nano-defect porous carbon material with high bonding BS content, as well as its preparation method and electrocatalytic use. Background technology:

[0002] Precious metal catalysts, such as platinum-based and palladium-based catalysts, have high ORR activity and excellent hydrogen peroxide selectivity in a wide range of pH values. However, their low surface content and high commercial cost severely limit their large-scale application in practical production. In recent years, carbon materials have been considered as very promising catalysts for the electrosynthesis of hydrogen peroxide due to their low cost, high reproducibility, adjustable nanostructure, and abundant edge defects. Increasing the ORR reaction active sites by introducing heteroatoms (boron, nitrogen, phosphorus, fluorine) or functional groups (oxygen functional groups) at the defects rich in carbon materials has been confirmed by numerous studies to be a reliable method to improve ORR activity and hydrogen peroxide selectivity.

[0003] Recently, many studies have shown that double heteroatom doping of electrocatalysts can effectively improve their reaction activity and selectivity of target products. This is largely attributed to the fact that double heteroatom doping can add more reactive sites to the electrocatalyst, and that the double heteroatoms produce a synergistic effect to promote the reaction. At the same time, heteroatoms such as boron atoms can stabilize the electronic structure of the catalyst during the electroreduction process, thereby enhancing the long-term stability of the catalyst. In order to further improve the catalytic performance of carbon materials in ORR, many researchers have begun to dope carbon materials with double heteroatoms. Among them, the highest selectivity of nitrogen / fluorine co-doped carbon material electrocatalysts for hydrogen peroxide in an alkaline electrolyte environment can reach 89.6%.

[0004] However, current diatomic-doped electrocatalysts for the ORR to hydrogen peroxide suffer from limitations such as high onset potentials and low activity and selectivity. Our boron- and sulfur-co-doped BS-C material demonstrates superior ORR performance. This material exhibits high selectivity and activity for the electrocatalytic ORR to hydrogen peroxide, along with a low onset potential. Furthermore, this material is simple to prepare and exhibits excellent stability, demonstrating its potential for practical production. Summary of the invention:

[0005] The object of the present invention is to provide a nano-defect porous carbon material with a high bonding BS content (hereinafter referred to as BS-C) and its preparation method and application. The principle of high-temperature annealing under inert gas is utilized, a tubular furnace is used to achieve the preparation effect, and a one-step method is adopted for preparation. The material improves the ORR activity of the porous defect carbon material in a manner that it is rich in BS active sites and the porous defect structure exposes more active sites for reacting with oxygen. In the synthesis, sodium lignin sulfonate is a precursor of C and S. Boric acid is added as a boron source and a promoter of the porous defect structure. The addition of excess boric acid contributes to the formation of BS active sites. A large number of BS active sites and a high-density porous defect structure provide numerous reaction active sites for ORR, which is beneficial to the efficient production of hydrogen peroxide by electrocatalytic ORR. At the same time, excess boric acid can promote the generation of porous defect structures of BS-C.

[0006] The technical solution of the present invention is: a nano-defect porous carbon material with a high bonding BS content, wherein the B element content in the material reaches 1.5at%-6at%, the S element content reaches 0.5at%-2at%, and the material has micropores <2nm, mesopores 2nm-50nm and macropores >50nm, and a specific surface area of 700m 2 g -1 -1300m 2 g -1 ; Using lignin sulfonate as a carbon source and boric acid as a boron source, a precursor is prepared after pretreatment, and the precursor is subjected to high-temperature annealing treatment to prepare a nano-defect porous carbon material with a high BS content; the viscosity of the lignin sulfonate is ≤200mPa.s.

[0007] The method for preparing the nano-defect porous carbon material with a high bonding BS content uses lignin sulfonate as a carbon source and boric acid as a boron source, prepares a precursor after pretreatment, and performs high-temperature annealing on the precursor to prepare the nano-defect porous carbon material with a high BS content.

[0008] The specific steps are as follows: sodium lignin sulfonate is added to a hot boric acid solution to form a mixed solution; the C and S elements in the carbon source and the B element in the boron source are uniformly mixed by long-term water bath heating and stirring; the mixed solution is heated and stirred in a water bath and the water is evaporated to dryness, the solid is completely dried, and then the large solid pieces are ground into fine powder. The resulting solid is the precursor; under the protection of a non-reactive gas, the above-mentioned precursor is subjected to a high-temperature annealing treatment to carbonize the precursor, and then the impurities in the material are washed away with boiling distilled water, and the material is filtered and vacuum dried to prepare a nano-defect porous carbon material with a high BS content.

[0009] The boric acid used is used as a boron source, and the ratio of the boric acid to the carbon source is 1 to 8:1.

[0010] The water bath temperature is 80°C, the stirring condition is 300-800 rpm, and the stirring time is 10-14 h.

[0011] The drying temperature is 70℃-90℃, and the drying time is 2h-6h.

[0012] The annealing process uses a tube furnace and the non-reactive gases are Ar and N2.

[0013] During the annealing process, the heating rate is 2°C to 15°C / min, the annealing temperature is 700°C to 1000°C, and the annealing time is 4h to 8h.

[0014] After washing with boiling distilled water to remove excess impurities, the material is filtered using a 0.45um filter membrane; the washed and filtered material is dried in a vacuum drying oven with a vacuum degree of -0.09MPa to -0.1MPa, a temperature of 30-50°C, and a time of 2-5h.

[0015] The application of the nano-defective porous carbon material with high bonding BS content in the electrocatalytic oxygen reduction reaction to prepare hydrogen peroxide.

[0016] Beneficial effects:

[0017] 1. The preparation method of the present invention is simple and efficient, and it not only efficiently introduces bonding diheteroatoms, but also retains the advantages of excellent electrical conductivity and high defect density of carbon materials, thus giving the material excellent catalytic performance for electrocatalytic oxygen reduction to produce hydrogen peroxide.

[0018] 2. Using a one-step preparation method, a carbon material with abundant nano-defects and pores was synthesized. The material has high B and S content and a large number of catalytic active sites with a special BS structure. The method is simple and efficient.

[0019] 3. The selectivity of the BS-C material of the present invention in electrocatalyzing O2 to produce H2O2 is 80%-95% in the voltage range of 0.4V-0.7V, and the electron transfer number is calculated to be around 2.12, which has a very high 2e - Selectivity; catalytic activity (expressed by the ring current density in the rotating disk test) is 0.4-0.75 mA cm -2 By varying the mass ratio of boric acid to sodium lignin sulfonate, the boron and sulfur content, pore structure, and specific surface area of the carbon BS-C material were controlled, thereby varying its electrocatalytic oxygen reduction performance. When boron was not used as a B source to dope the carbon material, the ORR activity and hydrogen peroxide selectivity of the carbon material decreased significantly.

[0020] 4. The BS-C material of the present invention can maintain long-term current stability and high Faradaic efficiency (FE) in long-term stability tests, which is better than many previously reported carbon-based materials. Description of the drawings:

[0021] Figure 1 High-resolution transmission electron microscopy (TEM) and Fast Fourier transform (FFT) images of a nano-defective porous carbon material with a high BS content. Analysis of the data in the images shows that at a standard 5nm scale, the material is locally well-graphitized, with a graphene-specific 0.343nm lattice spacing. In addition to the ordered structure, local defects in the graphene sheets are also present. Fast Fourier transform analysis reveals a lattice spacing variation of 0.355nm, indicating the formation of nanoscale defects.

[0022] Figure 2 The figure shows the test data of materials using different B source and C source ratios, 0:1, 2:1, 4:1, 8:1 I D / I G The values are 0.95, 1.0, 0.98, and 0.89, respectively, indicating that the material contains a large number of defect structures.

[0023] Figure 3 The BET surface area data of the material is shown in the figure. The figure shows the test data of the material using different ratios of B source to C source. According to the data analysis in the figure, the material has a large specific surface area and forms a porous structure. Figure 4 This graph shows the pore diameter and pore volume data for the material. The graph shows the distribution of pores in the 0-2nm, 2-50nm, and >50nm ranges. Analysis of the data in the graph indicates that the material has a rich structure of micropores, mesopores, and macropores.

[0024] Figure 5 This graph shows X-ray photoelectron spectroscopy (XPS) data for the material. It shows the boron and sulfur content in the material at different boron-to-carbon source ratios. SC, BS-C-1, BS-C-2, and BS-C-3 represent boron-to-carbon source ratios of 0:1, 2:1, 4:1, and 6:1, respectively. Analysis of the data in the graph indicates that the material is rich in boron and sulfur.

[0025] Figure 6 The LSV electrochemical data of the material are plotted. The graph shows the electrochemical ring current intensity and disk current intensity of the material at different boron source to carbon source ratios. Analysis of the data in the graph shows that the material has extremely high catalytic activity in the electrocatalytic oxygen reduction reaction to produce hydrogen peroxide.

[0026] Figure 7 The graph below shows the material's hydrogen peroxide selectivity. The graph shows the material's hydrogen peroxide selectivity over a voltage range of 0-0.8V at varying boron source to carbon source ratios. Analysis of the data in the graph indicates that the material exhibits high hydrogen peroxide selectivity in the electrocatalytic oxygen reduction reaction.

[0027] Figure 8 This graph shows the material's long-term stability. It illustrates the current changes and selectivity changes over a 12-hour period using a rotating ring-disk electrode. Analysis of the data in the graph indicates that both the ring and disk currents maintain excellent stability over the 12-hour period, while also maintaining selectivity above 85%. Specific implementation method:

[0028] Sodium lignin sulfonate is used as a carbon source and boric acid as a boron source. After pretreatment, a precursor is prepared. The precursor is then subjected to high-temperature annealing in a tube furnace to prepare a nano-defective porous carbon material with a high BS content. An appropriate amount of boric acid is dissolved in hot distilled water, and sodium lignin sulfonate is then added to the hot boric acid solution to form a mixed solution. The carbon and sulfur elements in the carbon source and the boron element in the boron source are uniformly mixed through prolonged water bath heating and magnetic stirring. The mixed solution is heated and stirred in a water bath and evaporated to dryness. The solid is placed in a forced air oven to thoroughly evaporate the remaining water. The bulk solid is then ground into a fine powder using an agate mortar. The resulting solid is the precursor. Under the protection of an inert gas, the precursor is subjected to high-temperature annealing in a tube furnace to carbonize the precursor. The carbonized precursor is then washed with boiling distilled water to remove excess boric acid, boron oxide, sulfur, and other impurities. The mixture is then filtered and vacuum dried to prepare BS-C, a nano-defective porous carbon material with a high BS content.

[0029] The C and S sources of the material are sodium lignin sulfonate, which contains -SO3 - , low viscosity ≤ 200mPa.s,

[0030] The B source of the material is boric acid.

[0031] The mass ratio of the boric acid (source B) to the sodium lignin sulfonate (source C) is 1:1, 2:1, 3:1, 4:1, 6:1, and 8:1.

[0032] The stirring condition is 300-800 rpm, and the stirring time is 10-14 h.

[0033] The precursor drying conditions are blower drying, drying temperature is 70° C.-90° C., and drying time is 2-6 hours.

[0034] The annealing process was carried out under nitrogen atmosphere, and the heating rates were 2°C / min, 5°C / min, 10°C / min, and 15°C / min.

[0035] The annealing condition is 700-1000° C., and the annealing time is 4-8 hours.

[0036] The washing and filtration process uses boiling distilled water and the filtration membrane is 0.45um.

[0037] The drying conditions after filtration are vacuum drying, with a vacuum degree of -0.09MPa to -0.1MPa, a temperature of 30-50°C, and a time of 2h-5h.

[0038] The prepared material BS-C has a B content of 1.5 at % to 6 at %, and an S content of 0.5 at % to 2 at %.

[0039] The prepared material BS-C contains micropores (<2nm), mesopores (2nm-50nm) and macropores (>50nm), with a specific surface area of 700m 2 g -1 -1300m 2 g -1 .

[0040] The prepared material BS-C is used in the electrocatalytic oxygen reduction reaction to produce hydrogen peroxide. The electrocatalytic efficiency is 80%-95% in the voltage range of 0.4V-0.7V, the electron transfer number is calculated to be around 2.12, and the catalytic activity (expressed by the ring current density in the rotating disk test) is 0.4-0.75mA·cm -2 , the starting potential is 0.7V-0.8V.

[0041] Example 1: The mass ratio of boric acid to precursor sodium lignin sulfonate is 2:1 for the nano-defect porous carbon material with high BS content

[0042] 2g of boric acid and 1g of sodium lignin sulfonate were added to 80°C distilled water and stirred at 600rpm in a constant temperature water bath at 80°C for 12h until the mixture was evenly mixed and 5 / 6 of the water volume evaporated. The remaining water was then thoroughly evaporated in a forced air oven at 80°C and ground into a fine powder in a mortar to prepare a precursor. The dried powder was heated at 900°C in a tube furnace under a protective atmosphere of N2 gas for 5h at a heating rate of 5°C / min. After cooling to room temperature, the remaining sulfur in the carbon material was washed away with 500ml of boiling distilled water to prepare a porous carbon material with high catalytic performance. The catalytic activity (expressed by the ring current in the rotating disk test) was 0.51mA·cm -2 , the selectivity for hydrogen peroxide is 77%-88% and the onset potential is -0.76V.

[0043] Example 2: The mass ratio of boric acid to precursor sodium lignin sulfonate is 4:1 for the nano-defective porous carbon material with high BS content

[0044] 4g of boric acid and 1g of sodium lignin sulfonate were added to 80°C distilled water and stirred at 600rpm in a constant temperature water bath at 80°C for 12h until the mixture was evenly mixed and 5 / 6 of the water volume evaporated. The remaining water was then thoroughly evaporated in a forced air oven at 80°C and ground into a fine powder in a mortar to prepare a precursor. The dried powder was heated at 900°C in a tube furnace under a protective atmosphere of N2 gas for 5h at a heating rate of 5°C / min. After cooling to room temperature, the remaining sulfur in the carbon material was washed away with 500ml of boiling distilled water to prepare a porous carbon material with high catalytic performance. The catalytic activity (expressed by the ring current in the rotating disk test) was 0.58mA·cm -2 , the selectivity for hydrogen peroxide is 78%-83% and the onset potential is -0.82V.

[0045] Example 3: The mass ratio of boric acid and sodium lignin sulfonate for the nano-defect porous carbon material with high BS content is 8:1

[0046] 8g of boric acid and 1g of sodium lignin sulfonate were added to 80°C distilled water and stirred at 600rpm in a constant temperature water bath at 80°C for 12h until the mixture was evenly mixed and 5 / 6 of the water volume evaporated. The remaining water was then thoroughly evaporated in a forced air oven at 80°C and ground into a fine powder in a mortar to prepare a precursor. The dried powder was heated at 900°C in a tube furnace under a protective atmosphere of N2 gas for 5h at a heating rate of 5°C / min. After cooling to room temperature, the remaining sulfur in the carbon material was washed away with 500ml of boiling distilled water to prepare a porous carbon material with high catalytic performance. The catalytic activity (expressed by the ring current in the rotating disk test) was 0.76mA·cm -2 , the selectivity for hydrogen peroxide is 87%-93% and the onset potential is -0.78V.

[0047] Comparative Example 1: Boric acid and lignin were used in a mass ratio of 8:1

[0048] 8g of boric acid and 1g of lignin were added to 80°C distilled water. The mixture was stirred at 600rpm in a constant temperature water bath at 80°C for 12 hours until the mixture was evenly mixed and 5 / 6 of the water volume evaporated. The remaining water was then thoroughly evaporated in a forced air oven at 80°C and ground into a fine powder in a mortar to prepare a precursor. The dried powder was heated at 900°C in a tube furnace under a protective atmosphere of N2 gas for 5 hours at a heating rate of 5°C / min. After cooling to room temperature, the remaining sulfur in the carbon material was washed away with 500ml of boiling distilled water to prepare a porous carbon material with high catalytic performance. The catalytic activity (expressed by the ring current in the rotating disk test) was 0.39mA·cm -2 The selectivity for hydrogen peroxide is 37%-83%, and the starting potential is -0.8 V. Comparative Example 2: The mass ratio of boric acid to precursor sodium lignin sulfonate is 0:1.

[0049] 1g of sodium lignin sulfonate was dissolved in 80°C distilled water and stirred in a constant temperature water bath at 80°C at 600 rpm for 12 hours to evenly mix and evaporate 5 / 6 of the water volume. The remaining water was then thoroughly evaporated in a forced air oven at 80°C and ground into a fine powder in a mortar to prepare a precursor. The dried powder was heated in a tube furnace at 900°C for 5 hours in a protective atmosphere of N2 gas at a heating rate of 5°C / min. After cooling to room temperature, the remaining sulfur in the carbon material was washed away with 500ml of boiling distilled water to prepare a porous carbon material with high catalytic performance. The catalytic activity (expressed by the ring current in the rotating disk test) was 0.67mA·cm -2 , the selectivity for hydrogen peroxide is 66%-84% and the onset potential is -0.75 V.

Claims

1. A nano-defective porous carbon material with a high bonding BS content, characterized in that: The B content in the material reaches 1.5at%-6at%, the S content reaches 0.5at%-2at%, and the material has micropores <2nm, mesopores 2nm-50nm and macropores >50nm, with a specific surface area of 700m 2 g -1 -1300m 2 g -1 ; Using lignin sulfonate as a carbon source and boric acid as a boron source, a precursor is prepared after pretreatment, and the precursor is subjected to high-temperature annealing treatment to prepare a nano-defect porous carbon material with a high BS content; the viscosity of the lignin sulfonate is ≤200mPa.s.

2. The method for preparing the nano-defect porous carbon material with high bonding BS content according to claim 1, characterized in that: Lignin sulfonate is used as a carbon source and boric acid is used as a boron source. A precursor is prepared after pretreatment, and the precursor is subjected to high-temperature annealing to prepare a nano-defect porous carbon material with a high BS content.

3. The method for preparing a nano-defect porous carbon material with a high bonding BS content according to claim 2, wherein: The specific steps are as follows: sodium lignin sulfonate is added to a hot boric acid solution to form a mixed solution; the C and S elements in the carbon source and the B element in the boron source are uniformly mixed by long-term water bath heating and stirring; the mixed solution is heated and stirred in a water bath and the water is evaporated to dryness, the solid is completely dried, and then the large solid pieces are ground into fine powder. The resulting solid is the precursor; under the protection of a non-reactive gas, the above-mentioned precursor is subjected to a high-temperature annealing treatment to carbonize the precursor, and then the impurities in the material are washed away with boiling distilled water, and the material is filtered and vacuum dried to prepare a nano-defect porous carbon material with a high BS content.

4. The method for preparing a nano-defect porous carbon material with a high bonding BS content according to claim 3, wherein: The ratio of boric acid used as a boron source to a carbon source is 1 to 8:

1.

5. The method for preparing a nano-defect porous carbon material with a high bonding BS content according to claim 3, wherein: The water bath temperature is 80°C, the stirring condition is 300-800 rpm, and the stirring time is 10-14 h.

6. The method for preparing a nano-defect porous carbon material with a high bonding BS content according to claim 3, wherein: The drying temperature is 70℃-90℃, and the drying time is 2h-6h.

7. The method for preparing a nano-defect porous carbon material with a high bonding BS content according to claim 3, wherein: The annealing process uses a tube furnace and the non-reactive gases are Ar and N2.

8. The method for preparing a nano-defect porous carbon material with a high bonding BS content according to claim 3, wherein: During the annealing process, the heating rate is 2°C to 15°C / min, the annealing temperature is 700°C to 1000°C, and the annealing time is 4h to 8h.

9. The method for preparing a nano-defect porous carbon material with a high bonding BS content according to claim 3, wherein: After washing with boiling distilled water to remove excess impurities, the material was filtered using a 0.45 μm filter membrane; the washed and filtered material was dried in a vacuum drying oven with a vacuum degree of -0.09 MPa to -0.1 MPa, a temperature of 30-50°C, and a time of 2-5 hours.

10. Use of the nano-defective porous carbon material with high bonding BS content according to claim 1 in the electrocatalytic oxygen reduction reaction to produce hydrogen peroxide.

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