Preparation method and application of cobalt metal nanoparticle loaded boron-nitrogen co-doped sp2 / sp3 composite carbon material

Abstract

The invention discloses a preparation method and application of a cobalt metal nanoparticle loaded boron-nitrogen co-doped sp2 / sp3 composite carbon material. According to the method, chitosan is used as a carbon / nitrogen bifunctional precursor, boric acid is used as a boron source, cobalt salt is used as an sp2-C forming accelerant and a metal cobalt source at the same time, and molecular-level uniform mixing is achieved through a sol-gel method. The preparation method comprises the following steps: heating and stirring to obtain a xerogel precursor, annealing in an inert atmosphere, constructing an sp2 / sp3 composite carbon skeleton through a cobalt catalytic graphitization mechanism, synchronously realizing boron-nitrogen co-doping and in-situ anchoring of cobalt nanoparticles, and washing and purifying to obtain the Co / BNC catalyst with high-dispersion active sites. Atomic-scale dispersion of the metal nanoparticles can be achieved through the coordination effect of amino in chitosan molecules and cobalt ions. The sp2 / sp3 hybridization proportion is regulated and controlled through graphitization of a cobalt catalytic carbon layer, and an electron conduction network is optimized. The obtained catalyst has high catalytic activity and stability when applied to electro-catalysis nitrate reduction.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrocatalyst preparation, and particularly relates to a cobalt metal nanoparticle loaded with boron and nitrogen co-doped sp 2 / sp 3 Preparation methods and applications of composite carbon materials. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance understanding of the overall background of the invention and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to those skilled in the art.

[0003] Carbon materials have become a promising non-precious metal catalyst in the field of electrocatalysis due to their tunable electronic structure, high chemical stability and abundant surface active sites. In recent years, the carbon materials have been widely used in the field of electrocatalysis through heteroatom doping (such as nitrogen, boron, sulfur, etc.) and carbon crystal structure regulation (sp 2 / sp 3 The construction of high-performance carbon-based catalysts (by optimizing the ratio) has become a research hotspot for replacing precious metal materials.

[0004] However, the existing technology still faces the following key problems: (1) Although single heteroatom doping (such as nitrogen doping) can introduce active sites, its ability to adsorb / activate intermediates in complex catalytic reactions (such as nitrate reduction, oxygen reduction, etc.) is limited. For example, although the pyridinic nitrogen site in traditional nitrogen-doped carbon materials (NC) can promote oxygen reduction reaction (ORR), it has no effect on nitrate (NO3 - ) has a weak adsorption capacity. Boron-nitrogen co-doping (BNC) can enhance the adsorption capacity of oxygen-containing species by forming BNC synergistic sites, but the existing methods are difficult to achieve uniform co-doping of boron / nitrogen atoms, resulting in limited active site density. (2) sp 2 Carbon (graphitized structure) provides high electrical conductivity, sp 3 Carbon (amorphous structure) is rich in defect sites, and the ratio of the two directly affects the charge transfer and active site exposure of the catalyst. 2 structure, while low temperature preparation leads to sp 3 The ratio is too high and the conductivity decreases. Studies have shown that metal-catalyzed graphitization can precisely control sp 2 / sp 3ratio, but the metal particles in the existing technology are prone to agglomeration (>10nm), resulting in uneven distribution of catalytic sites. (3) Loading metal nanoparticles (such as cobalt) can further enhance the intrinsic activity of carbon materials, but conventional impregnation or physical mixing methods easily lead to sintering of metal particles (the particle size increases to 5-10nm during annealing), and lack strong electronic coupling with the carbon support. For example, cobalt particles in Co / NC catalysts often exist in a metallic state, and weak interactions with the carbon matrix limit the charge transfer efficiency. (4) Although precious metal catalysts (such as Pt, Ru) have high activity, their scarcity and easy poisoning properties limit their large-scale application. Existing non-metallic carbon-based catalysts (such as doped graphene) are prone to structural degradation in strong acid / alkaline environments, and the preparation process often relies on expensive precursors (such as cyanamide, ionic liquids, etc.).

[0005] In summary, achieving the coordinated optimization of catalytically active sites and conductive networks in multi-heteroatom doped systems has become a core challenge in current research. Although extensive research has been devoted to optimizing heteroatom doping strategies, carbon-based catalysts that can simultaneously achieve high catalytic activity and excellent conductivity remain rare.

[0006] In the field of nitrate reduction to produce ammonia, the existing technology provides technical solutions such as "catalytic materials are metal elements, metal sulfides, metal selenides, metal phosphides, metal nitrides, and boron-doped diamonds", but there are obvious problems of low Faraday efficiency and low conversion rate. Summary of the Invention

[0007] In view of the shortcomings of the prior art, the present invention provides a cobalt metal nanoparticle loaded with boron and nitrogen co-doped sp 2 / sp 3 Preparation method and application of composite carbon materials. The innovation of this invention is to construct sp through cobalt catalyzed graphitization strategy. 2 / sp 3 The composite carbon skeleton, combined with the triple synergistic effect of boron-nitrogen co-doping and metal nanoparticle loading, breaks through the existing technological bottleneck.

[0008] The purpose of this invention is to propose an innovative strategy to achieve simultaneous boron-nitrogen co-doping and sp- 2 / sp 3 Precise control of carbon structure. Specifically, by utilizing the nitrogen-rich properties of chitosan, the controllable doping ability of boric acid, and the in-situ confinement of cobalt salts, the following synergistic effect is formed during the pyrolysis process: B atoms replace the carbon lattice to form BC bonds, and N atoms construct pyridine / graphitic nitrogen structures. The two synergistically optimize the adsorption energy of the intermediate sp 2 / sp 3 Composite framework, cobalt nanoparticles (10-25nm) induce local graphitization, forming sp 2 Conductive network and sp3 The staggered structure of the defective regions strengthens the metal-support interaction, and the cobalt nanoparticles and B / N-doped carbon generate electronic coupling, improving the charge transfer efficiency. This method overcomes the technical bottleneck of traditional doped carbon materials with a single active site and poor metal dispersion, providing new ideas for the design of efficient and stable carbon-based electrocatalysts.

[0009] In order to achieve the above object, the technical solution of the present invention is:

[0010] As a first aspect of the present invention, there is provided a cobalt metal nanoparticle loaded with boron and nitrogen co-doped sp 2 / sp 3 The preparation method of the composite carbon material comprises the following steps:

[0011] Step 1: dissolving chitosan, boric acid and cobalt salt in an aqueous solution to form a uniformly mixed precursor solution; stirring the resulting solution, evaporating it to dryness, and drying it to obtain a xerogel precursor;

[0012] Step 2: The dry gel precursor prepared in step 1 is subjected to programmed temperature annealing under an inert atmosphere to form sp 2 / sp 3 Composite carbon skeleton;

[0013] Step 3: washing the product by boiling with hydrochloric acid to remove unbound cobalt particles and boric acid, and drying to obtain a Co / BNC catalyst.

[0014] In this application, chitosan acts as a dual-functional carrier of biomass carbon precursor and self-doped nitrogen source: the abundant amino groups (-NH2) and hydroxyl groups (-OH) in its molecular chain form a cross-linked network through deacetylation during the pyrolysis process, inhibiting the disordered shrinkage of the carbon skeleton; on the other hand, the amino groups generate pyridine nitrogen and graphitic nitrogen active sites after pyrolysis.

[0015] On the other hand, as a N source, compared with starch, chitosan exhibits unique coordination regulation advantages: the synergistic effect of amino (-NH2) and hydroxyl (-OH) groups within its molecules can achieve dual precise regulation of in situ nitrogen doping and the coordination environment of metal Co atoms.

[0016] In one embodiment of the present invention, the specific steps are as follows: first, boric acid is dissolved in hot water, then chitosan and a cobalt salt are added to the boric acid solution. Under acidic conditions (boric acid solution), the chitosan dissolves and forms a viscous sol, and the cobalt ions are evenly dispersed between the chitosan molecular chains through coordination; a uniformly mixed precursor solution is formed through a sol-gel method; the solution is evaporated to remove water by stirring; and the solution is thoroughly dried in an oven to obtain a uniform xerogel precursor. This step helps the cobalt metal and other components form a structure with uniform distribution.

[0017] In step 2, annealing is performed in an inert atmosphere to promote the catalytic graphitization of cobalt metal, thereby forming sp 2 / sp 3 Composite carbon skeleton. The microstructure of the catalyst can be effectively controlled by adjusting the annealing temperature and atmosphere.

[0018] In step 3, the unbound cobalt particles and boric acid are removed by boiling and washing with hydrochloric acid to obtain a high-purity catalyst.

[0019] In the Co / BNC catalyst obtained by the above steps, the average particle size of the cobalt metal nanoparticles is 10-50 nm, and sp 2 -C and sp 3 -C exist at the same time, and this structure gives the catalyst excellent electrocatalytic performance.

[0020] Preferably, the cobalt salt in step 1 is cobalt nitrate, cobalt acetate or cobalt chloride.

[0021] Preferably, in step 1, the mass ratio of chitosan, boric acid and cobalt salt used is 1:0.5-2:0.1-0.5. Under this material ratio, the prepared cobalt metal nanoparticles loaded with boron and nitrogen co-doped sp 2 / sp 3 The composite carbon material is used for the electrocatalytic nitrate reduction reaction to synthesize ammonia, with a high Faradaic efficiency of over 70%.

[0022] Furthermore, in one embodiment of the present invention, when the mass ratio of chitosan, boric acid and cobalt salt is 1:2:0.1, the Faradaic efficiency is high and can reach 98%.

[0023] Preferably, in step 1, the stirring temperature is 80-120° C., the stirring rate is 200-800 rpm, and the stirring time is 8-12 h; the drying temperature is 80-120° C., and the drying time is 8-12 h.

[0024] Preferably, in step 2, under the inert atmosphere, the inert gas is argon or nitrogen, and the gas flow rate is 10-50 mL / min.

[0025] Preferably, in step 2, the heating rate is 2-5°C / min, the annealing temperature is 800-1000°C, and the holding time is 2-4h.

[0026] Preferably, in step 3, the hydrochloric acid concentration is 0.1M-1M, the temperature is 100-120°C, and the drying temperature is 80-120°C.

[0027] The average particle size of cobalt nanoparticles in the obtained Co / BNC catalyst is 10-50nm, sp 2 -C and sp 3-C also exists.

[0028] In one or more embodiments of the present invention, the average particle size of the cobalt nanoparticles in the obtained Co / BNC catalyst is 10-50 nm.

[0029] In one or more embodiments of the present invention, the sp2 / sp3 ratio of cobalt nanoparticles in the obtained Co / BNC catalyst is 1.8-3.8.

[0030] The principle of the preparation method provided by the present invention is: chitosan is used as a carbon / nitrogen dual-functional precursor, boric acid is used as a boron source, and cobalt salt is used as a sp 2 -C forms a promoter and a metal cobalt source, and a uniform molecular mixing is achieved through the sol-gel method. After heating and stirring to obtain a dry gel precursor, it is annealed in an inert atmosphere to construct sp through the cobalt-catalyzed graphitization mechanism. 2 / sp 3 A composite carbon skeleton was prepared, and boron-nitrogen co-doping and in-situ anchoring of cobalt nanoparticles were simultaneously achieved. After water washing and purification, a Co / BNC catalyst with highly dispersed active sites was obtained.

[0031] The present invention utilizes the coordination effect between amino groups in chitosan molecules and cobalt ions to achieve atomic-level dispersion of metal nanoparticles; the sp 2 / sp 3 The hybrid ratio is optimized, and the electronic conduction network is optimized. The obtained catalyst has high catalytic activity and stability when applied to electrocatalytic nitrate reduction.

[0032] As a second aspect of the present invention, there is provided a cobalt metal nanoparticle loaded with boron and nitrogen co-doped sp 2 / sp 3 Preparation method of composite carbon material Cobalt metal nanoparticles loaded with boron and nitrogen co-doped sp 2 / sp 3 Composite carbon materials.

[0033] As a third aspect of the present invention, there is provided a cobalt metal nanoparticle loaded with boron and nitrogen co-doped sp 2 / sp 3 Preparation method of composite carbon material Cobalt metal nanoparticles loaded with boron and nitrogen co-doped sp 2 / sp 3 Application of composite carbon materials as catalysts in catalytic electrocatalytic reactions.

[0034] Furthermore, the present invention provides a cobalt metal nanoparticle loaded with boron and nitrogen co-doped sp 2 / sp 3 Preparation method of composite carbon material Cobalt metal nanoparticles loaded with boron and nitrogen co-doped sp 2 / sp 3 Application of composite carbon materials as catalysts in the electrocatalytic nitrate reduction reaction to synthesize ammonia.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] 1. The present invention provides a cobalt metal nanoparticle loaded with boron and nitrogen co-doped sp 2 / sp 3 The preparation method of the composite carbon material uses chitosan as a carbon source and a nitrogen source, boric acid as a boron source, and cobalt nitrate as a cobalt source, prepares a precursor after pretreatment, and performs a high-temperature annealing treatment in an inert gas to prepare cobalt metal nanoparticles loaded with boron and nitrogen co-doped sp 2 / sp 3 Composite carbon material (Co / BNC). The preparation method of the present invention is simple and has higher operability and lower equipment requirements compared with the traditional complex catalyst synthesis method. This method can not only achieve the sp 2 / sp 3 The ratio can be regulated, and the uniform distribution of cobalt metal nanoparticles and the controllability of particle size can be ensured, which greatly reduces the cost and technical threshold of catalyst preparation and has good potential for industrial application.

[0037] 2. The present invention precisely controls the ratio of each precursor raw material and the subsequent annealing conditions in the sol-gel method, and the average particle size of the obtained cobalt nanoparticles in the carbon matrix is ​​stably maintained between 10-50nm, effectively avoiding the problems of easy agglomeration of cobalt particles and uneven particle size distribution in traditional methods, and ensuring the efficient exposure and uniform distribution of active sites in the catalyst. Through the cobalt catalytic graphitization process, a catalyst with both sp 2 -C and sp 3 -C composite carbon architecture, in which sp 2 The carbon phase gives the material excellent electronic conductivity, which is conducive to the efficient transmission of electrons during the catalytic process; 3 The carbon phase enhances the structural stability and mechanical strength of the carbon material, and the two work synergistically to effectively improve the overall performance of the catalyst. Boron and nitrogen co-doping during the preparation process forms various chemical bonding sites, such as BN, BC, and NC. This significantly modulates the electron cloud density on the carbon support surface, optimizing the adsorption-dissociation behavior of the catalyst surface, thereby enhancing the adsorption capacity of nitrate ions and the stability of reaction intermediates, improving the efficiency of the catalytic reaction.

[0038] 3. The selectivity of the Co / BNC material for electrocatalytic nitrate reduction to ammonia synthesis is 65% to 98% within the voltage window of -0.6 to -0.1 V vs RHE, and the conversion rate is 462 to 4039 mg / (h cm 2), with ultra-high electrocatalytic nitrate reduction activity. By changing the addition of cobalt nitrate, boric acid and chitosan, the sp in carbon materials can be regulated. 2 / sp 3 The ratio of the elements changes the catalytic performance of electrocatalytic nitrate reduction to ammonia. 2 / sp 3 The activity of Co / BNC material for electrocatalytic nitrate reduction and the selectivity for ammonia decreased significantly when the catalyst was made of composite carbon material and chitosan was not used as nitrogen source.

[0039] 4. The Co / BNC catalyst of the present invention exhibits significant advantages in electrochemical stability tests. It can maintain a stable current density and high Faradaic efficiency under continuous operation conditions, and its comprehensive performance surpasses that of reported nitrogen-doped carbon and transition metal / carbon composites. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0041] Figure 1 This is a high-resolution transmission electron micrograph of the Co / BNC material prepared in Example 1. In the electron micrograph, it can be observed that the Co nanoparticles are evenly distributed in the sp 2 / sp 3 Composite carbon materials.

[0042] Figure 2 The cobalt metal nanoparticles prepared in Example 1 are loaded with boron and nitrogen co-doped sp 2 / sp 3 High-resolution transmission electron microscopy mapping of the composite carbon material. The mapping shows that Co, B, and N are evenly distributed on the surface of the carbon material.

[0043] Figure 3 The XRD spectra of the products obtained in Examples 1 to 3 and Comparative Example 1 are shown in the figure. 2 Carbon content is the highest, indicating that Co and boric acid can promote sp 2 Carbon production.

[0044] Figure 4 The Raman spectra of the product materials obtained in Examples 1 to 3 and Comparative Example 1 are shown in the figure. The Raman spectra of different materials are shown in the figure, indicating that the materials have rich defect structures.

[0045] Figure 5The LSV curves of the electrocatalytic nitrate reduction of the product materials obtained in Examples 1 to 3 and Comparative Example 1 are shown in the figure. The LSV curves of different materials are shown in the figure. From the data in the figure, it can be seen that the Co / BNC material has the best electrocatalytic nitrate reduction performance.

[0046] Figure 6 This is a Faradaic efficiency diagram of the Co / BNC material prepared in Example 1 for electrocatalytic nitrate reduction to ammonia. As can be seen from the figure, within the voltage window of -0.6 to -0.1 V vs RHE, the Faradaic efficiency is 65% to 98%, indicating ultra-high electrocatalytic nitrate reduction activity.

[0047] Figure 7 The conversion efficiency of electrocatalytic nitrate reduction to ammonia by the product materials obtained in Examples 1 to 3 and Comparative Example 1 is shown in the figure. It can be seen from the figure that the Co / BNC material has the highest conversion rate, with a conversion rate of 462 to 4039 mg / (h cm) in the voltage window of -0.6 to -0.1 V vs RHE. 2 ). DETAILED DESCRIPTION

[0048] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0049] The present invention provides a cobalt metal nanoparticle loaded with boron and nitrogen co-doped sp 2 / sp 3 Preparation method and application of composite carbon materials: chitosan, boric acid and cobalt salt are dissolved in deionized water and a sol-gel method is used to form a homogeneous mixture. The water in the solution is removed by stirring and evaporating; and then it is thoroughly dried in an oven to obtain a uniform dry gel precursor. This step can help the cobalt metal and other components form a uniformly distributed structure. Annealing treatment is carried out in an inert atmosphere to promote the catalytic graphitization of the cobalt metal, thereby forming sp 2 / sp 3 Composite carbon skeleton. By adjusting the annealing temperature and atmosphere, the microstructure of the catalyst can be effectively controlled. By boiling and washing with hydrochloric acid, unbound cobalt particles and boric acid are removed to obtain a high-purity catalyst. In the Co / BNC catalyst obtained by the above steps, the average particle size of the cobalt metal nanoparticles is 10-25nm, and sp 2 -C and sp 3 -C exist at the same time, and this structure gives the catalyst excellent electrocatalytic performance.

[0050] In the present invention, a uniformly mixed precursor solution is formed by the sol-gel method; the water in the solution is removed by stirring and evaporating. The sol-gel method is a method for synthesizing materials through solution chemical reactions. Its core is to form a three-dimensional network structure (sol) by hydrolysis and polycondensation of the precursor, and then convert it into a solid material (gel) by drying or heat treatment. Boric acid is dissolved in hot water, and then chitosan and cobalt salt (metal source) are added. Chitosan dissolves under acidic conditions (boric acid solution) and forms a viscous sol, and the cobalt ions are evenly dispersed between the chitosan molecular chains through coordination. When the water is evaporated by stirring, the sol gradually loses water and condenses to form a three-dimensional network gel cross-linked by the chitosan-cobalt complex. The drying process further solidifies the structure, and finally a dry gel precursor is obtained.

[0051] The ratio of chitosan, boric acid and cobalt salt used is: 1: (0.5-2): (0.1-0.5).

[0052] In the stirring and evaporating step, the stirring temperature is 80-120° C., the stirring rate is 200-800 rpm, and the stirring time is 8-12 h.

[0053] The drying temperature is 80-120° C., and the drying time is 8-12 hours.

[0054] The inert gas is argon or nitrogen, and the gas flow rate is 10-50 mL / min.

[0055] The heating rate is 2-5°C / min, the annealing temperature is 800-1000°C, and the holding time is 2-4h.

[0056] The hydrochloric acid concentration is 0.1M-1M, the temperature is 100-120°C, and the drying temperature is 80-120°C.

[0057] The average particle size of cobalt nanoparticles in the obtained Co / BNC catalyst is 10-25nm, sp 2 -C and sp 3 -C also exists.

[0058] The cobalt metal nanoparticles loaded with boron and nitrogen co-doped sp 2 / sp 3 Application of composite carbon material (Co / BNC) catalyst in electrocatalytic nitrate reduction to ammonia synthesis.

[0059] The selectivity of the Co / BNC material for electrocatalytic nitrate reduction to ammonia synthesis is 65% to 98% within the voltage window of -0.6 to -0.1 V vs RHE, and the conversion rate is 462 to 4039 mg / (h cm 2 ), with ultra-high electrocatalytic nitrate reduction activity.

[0060] The electrocatalytic reaction process is as follows: The experiment uses a three-electrode H-type electrolytic cell system with Co / BNC (1 mg / cm 2 ) was used as the working electrode, a mixed solution of 1 M KOH and 0.1 M KNO3 was used as the electrolyte, and the reaction was carried out in the potential window of -0.6 to -0.1 V vs RHE.

[0061] Example 1: Cobalt metal nanoparticles loaded with boron and nitrogen co-doped sp 2 / sp 3 Preparation of composite carbon materials

[0062] 2g chitosan and 0.2g cobalt nitrate were dissolved in a boric acid solution (boric acid addition amount was 4g), stirred at 400rpm and 90℃ for 10h, and the water was evaporated. Subsequently, the precursor was dried in an oven at 90℃ for 10h, and the obtained precursor was heated at 900℃ in a tube furnace under an Ar protective atmosphere for 4h with a heating rate of 2℃ / min. After cooling to room temperature, it was boiled and pickled with a 1M hydrochloric acid solution to remove excess boric acid and unbound cobalt impurities, and cobalt metal nanoparticles with high catalytic performance were prepared. 2 / sp 3 Composite carbon material (Co / BNC). The catalytic activity of electrocatalytic nitrate reduction to ammonia is 98% at -0.4 V vs RHE, with a conversion rate of 2641 mg / (h cm 2 ). High-resolution transmission electron microscopy images of Co / BNC materials are shown in Figure 2. Figure 1 As shown in the figure, the average particle size of cobalt nanoparticles is 10-25nm. Figure 2 As shown. 2 / sp 3 The ratio is 3.34.

[0063] Example 2: Cobalt metal nanoparticles loaded with nitrogen-doped sp 2 / sp 3 Preparation of composite carbon materials

[0064] The amount of boric acid added was 0g, 2g chitosan and 0.2g cobalt nitrate were dissolved in the aqueous solution, stirred at 400rpm and 90℃ for 10h, and the water was evaporated. Then, the precursor was dried in an oven at 90℃ for 10h. The obtained precursor was heated at 900℃ in a tube furnace under an Ar protective atmosphere for 4h at a heating rate of 2℃ / min. After cooling to room temperature, it was boiled and pickled with 1M hydrochloric acid solution to remove unbound cobalt impurities, and cobalt metal nanoparticles loaded with nitrogen-doped sp were prepared. 2 / sp 3Composite carbon material (Co / NC). The catalytic activity of electrocatalytic nitrate reduction to ammonia is 45% at -0.4V vs RHE, and the conversion rate is 2097mg / (hcm 2 ). The average particle size of cobalt nanoparticles is 30-40nm, sp 2 / sp 3 The ratio is 2.57.

[0065] Example 3: Cobalt metal nanoparticles loaded with boron-doped sp 2 / sp 3 Preparation of composite carbon materials

[0066] 2g starch and 0.2g cobalt nitrate were dissolved in a boric acid solution (boric acid addition amount was 4g), stirred at 400rpm and 90℃ for 10h, and the water was evaporated. Then, the precursor was dried in an oven at 90℃ for 10h. The obtained precursor was heated at 900℃ in a tube furnace under an Ar protective atmosphere for 4h at a heating rate of 2℃ / min. After cooling to room temperature, it was boiled and pickled with 1M hydrochloric acid solution to remove unbound cobalt impurities to prepare cobalt metal nanoparticles loaded with boron doped sp 2 / sp 3 Composite carbon material (Co / BC). The catalytic activity of electrocatalytic nitrate reduction to ammonia is 32% at -0.4V vs RHE, and the conversion rate is 1551mg / (hcm 2 ). The average particle size of cobalt nanoparticles is 30-40nm, sp 2 / sp 3 The main reasons for the low Faradaic efficiency can be attributed to the following synergistic effects: the large size of cobalt nanoparticles (30-40nm) leads to insufficient exposure of active sites and a uniform surface crystal face, which triggers competition for the hydrogen evolution side reaction; the carbon matrix sp 2 / sp 3 The imbalance of the ratio (2.88) makes the topological defect density insufficient, weakening the intermediate (*NO2 - )’s stable adsorption capacity; the lack of nitrogen atoms failed to effectively form the active structure of B-Co-NC, resulting in a decrease in electron transfer efficiency.

[0067] Comparative Example 1: Boron and nitrogen co-doped sp 2 / sp 3 Preparation of composite carbon materials

[0068] 2g chitosan was dissolved in a boric acid solution (boric acid addition amount was 4g), stirred at 400rpm, 90℃, for 10h, and its water was evaporated. Then it was dried in an oven at 90℃ for 10h. The obtained precursor was heated at 900℃ in a tube furnace under an Ar protective atmosphere for 4h at a heating rate of 2℃ / min. After cooling to room temperature, it was boiled and pickled with 1M hydrochloric acid solution to remove excess boric acid to prepare boron-nitrogen co-doped sp 2 / sp 3 Composite carbon material (BNC). The catalytic activity of electrocatalytic nitrate reduction to ammonia is 41% at -0.4 V vs RHE, and the conversion rate is 1212 mg / (h cm 2 ). sp 2 / sp 3 The ratio is 1.31.

[0069] The XRD spectra, Raman spectra, LSV curves of electrocatalytic nitrate reduction, Faraday efficiency diagrams, and conversion efficiency diagrams of electrocatalytic nitrate reduction to ammonia of the products obtained in Examples 1 to 3 and Comparative Example 1 are shown in FIG. Figures 3 to 7 shown.

[0070] Example 4,

[0071] 2g chitosan, 1g boric acid, and 0.2g cobalt nitrate were dissolved in an aqueous solution and stirred at 400rpm and 90℃ for 10h, and the water was evaporated. The precursor was then dried in an oven at 90℃ for 10h. The resulting precursor was heated at 900℃ in a tube furnace under an Ar protective atmosphere for 4h at a heating rate of 2℃ / min. After cooling to room temperature, it was boiled and pickled with 1M hydrochloric acid solution to remove unbound cobalt impurities, and cobalt metal nanoparticles loaded with boron and nitrogen co-doped sp were prepared. 2 / sp 3 Composite carbon material (Co / BNC-1). The catalytic activity of electrocatalytic nitrate reduction to ammonia is 72% at -0.4 V vs RHE, with a conversion rate of 1429 mg / (hcm 2 ). The average particle size of cobalt nanoparticles is 10-20nm, sp 2 / sp 3 The ratio is 1.8.

[0072] Example 5,

[0073] 2g chitosan, 4g boric acid, and 1g cobalt nitrate were dissolved in an aqueous solution and stirred at 400rpm and 90℃ for 10h, and the water was evaporated. The precursor was then dried in an oven at 90℃ for 10h. The resulting precursor was heated at 900℃ in a tube furnace under an Ar atmosphere for 4h at a heating rate of 2℃ / min. After cooling to room temperature, it was boiled and pickled with 1M hydrochloric acid solution to remove unbound cobalt impurities, thereby preparing cobalt metal nanoparticles loaded with boron and nitrogen co-doped sp 2 / sp 3 Composite carbon material (Co / BNC-2). The catalytic activity of electrocatalytic nitrate reduction to ammonia is 77% at -0.4 V vs RHE, with a conversion rate of 1679 mg / (hcm 2 ). The average particle size of cobalt nanoparticles is 40-50nm, sp 2 / sp 3 The ratio is 3.8.

[0074] According to the Raman characterization results, it can be obtained that when sp 2 / sp 3 When the ratio is 3.34, the electrocatalytic nitrate reduction has the best catalytic activity (Faraday efficiency is 98%, conversion rate is 2641 mg / (h cm2)). 2 / sp 3 The activity is usually highest when the ratio is 1.8-3.8, and the material has both: sufficient sp 2 Ordered domains ensure electron conduction; moderate defects (sp 3 or edges) provide active sites.

[0075] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A cobalt metal nanoparticle loaded with boron and nitrogen co-doped sp 2 / sp 3 The method for preparing a composite carbon material is characterized in that: The steps include: Step 1: dissolving chitosan, boric acid and cobalt salt in an aqueous solution to form a uniformly mixed precursor solution; stirring the resulting solution, evaporating it to dryness, and drying it to obtain a xerogel precursor; Step 2: The dry gel precursor prepared in step 1 is subjected to programmed temperature annealing under an inert atmosphere to form sp 2 / sp 3 Composite carbon skeleton; Step 3: The product of step 2 is washed by boiling with hydrochloric acid to remove unbound cobalt particles and boric acid, and then dried to obtain a Co / BNC catalyst.

2. The cobalt metal nanoparticles loaded with boron and nitrogen co-doped sp 2 / sp 3 The method for preparing a composite carbon material is characterized in that: The cobalt salt in step 1 is at least one of cobalt nitrate, cobalt acetate or cobalt chloride.

3. The cobalt metal nanoparticles loaded with boron and nitrogen co-doped sp 2 / sp 3 The method for preparing a composite carbon material is characterized in that: In step 1, the ratio of chitosan, boric acid and cobalt salt used is 1:0.5-2:0.1-0.

5.

4. The cobalt metal nanoparticles loaded with boron and nitrogen co-doped sp 2 / sp 3 The method for preparing a composite carbon material is characterized in that: In step 1, the stirring temperature is 80-120° C., the stirring rate is 200-800 rpm, and the stirring time is 8-12 h; the drying temperature is 80-120° C., and the drying time is 8-12 h.

5. The cobalt metal nanoparticles loaded with boron and nitrogen co-doped sp 2 / sp 3 The method for preparing a composite carbon material is characterized in that: In step 2, under an inert atmosphere, the inert gas is argon or nitrogen, and the gas flow rate is 10-50 mL / min.

6. The cobalt metal nanoparticles loaded with boron and nitrogen co-doped sp 2 / sp 3 The method for preparing a composite carbon material is characterized in that: In step 2, the heating rate is 2-5°C / min, the annealing temperature is 800-1000°C, and the holding time is 2-4h.

7. The cobalt metal nanoparticles loaded with boron and nitrogen co-doped sp 2 / sp 3 The method for preparing a composite carbon material is characterized in that: In step 3, the concentration of hydrochloric acid is 0.1M-1M, the boiling temperature is 100-120°C, and the drying temperature is 80-120°C.

8. The cobalt metal nanoparticles loaded with boron and nitrogen co-doped sp 2 / sp 3 Preparation method of composite carbon material Cobalt metal nanoparticles loaded with boron and nitrogen co-doped sp 2 / sp 3 Composite carbon materials.

9. The cobalt metal nanoparticles loaded with boron and nitrogen co-doped sp 2 / sp 3 A composite carbon material, characterized in that The sp of cobalt nanoparticles in the obtained Co / BNC catalyst 2 / sp 3 The ratio is 1.8-3.

8.

10. The cobalt metal nanoparticles loaded with boron and nitrogen co-doped sp 2 / sp 3 Preparation method of composite carbon material Cobalt metal nanoparticles loaded with boron and nitrogen co-doped sp 2 / sp 3 Application of composite carbon materials as catalysts in catalytic electrocatalytic reactions.

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