Preparation method and application of N / O co-doped porous interconnected hollow carbon sphere catalyst

Abstract

The invention discloses a preparation method of an N / O co-doped porous interconnected hollow carbon sphere catalyst and application of the N / O co-doped porous interconnected hollow carbon sphere catalyst in efficient production of hydrogen peroxide through oxygen reduction reaction. The N / O co-doped hollow carbon sphere catalyst with a three-dimensional hierarchical porous structure is prepared by combining self-assembly with a high-temperature carbonization strategy. The synthesis process has the outstanding advantages of simplicity in operation, low cost, greenness, sustainability and the like. The obtained material has a unique three-dimensional hollow sphere structure, the nitrogen doping amount and the oxygen doping amount of the surface of the material respectively reach 37.28 at% and 12.65 at%, and rich active sites are provided for a 2e-ORR path. Experimental results show that the catalyst shows excellent 2e-ORR catalytic activity, the highest H2O2 selectivity of the catalyst can reach 94.3%, and good current efficiency and selectivity stability can still be kept after continuous operation for 10 h.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation of nano-carbon-based catalytic materials, and particularly relates to a preparation method and application of an N / O co-doped porous interconnected hollow carbon sphere catalyst. Background Art

[0002] Hydrogen peroxide (H2O2), as a green oxidant, has important application values in the fields of chemical synthesis, environmental governance and new energy (Angew. Chem. Int. Ed. 2006, 45, 6962–6984; Sci. Bull. 2015, 60, 55–64). Currently, the industrial production of H2O2 mainly relies on the anthraquinone process, which involves multi-step reactions and separation processes, and requires additional costs to treat organic wastes (Adv. Funct. Mater. 2021, 31, 2104716). Driven by the urgent demand for environmental protection processes, the development of alternative H2O2 production technologies has become a research hotspot. Among them, the electrochemical production of H2O2 through the oxygen reduction reaction (ORR) is regarded as an effective alternative to the traditional anthraquinone process due to its advantages of greenness, low cost, continuity and on-site generation (ACS Energy Lett. 2020, 5, 1881–1892). However, the production of H2O2 by ORR still faces major challenges because ORR essentially involves two-electron (2e - ) pathways and four-electron (4e - ) pathways, and these two pathways compete with each other (ACS Sustainable Chem. Eng. 2018, 6, 311−317). ORR can reduce O2 to H2O2 through the 2e - pathway (O2 + 2H + + 2e- → H2O2), while the 4e - pathway mainly produces H2O (O2 + 4H + + 4e - → H2O). When these two pathways occur simultaneously and compete with each other, it often leads to a decrease in the selectivity of the catalyst for H2O2 (Chem. Rev. 2018, 118, 2302-2312).

[0003] In recent years, carbon-based materials have shown significant advantages in the field of electrochemically synthesizing hydrogen peroxide (H2O2), which is mainly due to their unique physical and chemical properties: typical sp 2Hybrid electronic structure, adjustable geometric configuration, high specific surface area, porous structure characteristics, excellent electronic conduction ability, and precisely tunable catalytic performance (J. Electroanal. Chem. 2020, 878, 114690). Research has shown that the electronic structure of active sites in carbon materials can be effectively regulated through heteroatom doping engineering (Electrochimica Acta. 2020), and the successful development of nitrogen-doped carbon nanotubes verifies the effectiveness of this strategy in promoting the four-electron (4e - ) oxygen reduction reaction (ORR) pathway (Science. 2009, 323, 760-764). However, the competitive mechanism between the two-electron (2e - ) and four-electron ORR (4e - ) pathways leads to a significant decrease in H2O2 selectivity, and this contradiction urgently needs to be resolved. In response to the problem of selective regulation, the multi-atom co-doping strategy exhibits unique advantages (ACS Catal. 2022, 12, 1288−1297). Compared with single heteroatom doping, the multi-doped system can induce stronger lattice distortion in the carbon lattice, and significantly increase the density of active sites through the synergistic polarization effect and spatial confinement effect (Chin. Chem. Lett. 2021, 32, 745-749). The research further reveals the key regulatory role of the composite active center formed by oxygen functional groups (such as carboxyl and epoxy groups) and carbon atoms in the 2e - ORR pathway. The positive correlation between the oxygen content of the catalyst established by its surface oxidation treatment technology and the H2O2 yield provides a new idea for selective optimization.

[0004] In terms of material structure design, the novel hollow carbon sphere structure breaks through the limitations of traditional one-dimensional carbon materials. This nano-reactor has two advantages: firstly, the confined microenvironment formed by the cavity structure can optimize the adsorption configuration of reactants; secondly, the three-dimensional interconnected pore system significantly improves the gas / liquid phase mass transfer efficiency (Angew. Chem. Int. Ed. 2020, 59, 18374 –18379; Nanoscale. 2020, 12, 16586–16595). Experiments have confirmed that this structural design not only improves the catalytic stability but also can regulate the adsorption energy of intermediate products through the interfacial effect, providing an innovative solution for industrial H2O2 production. In the current industrial system, platinum group noble metal (PGMs) catalysts still face the dual constraints of high cost and scarce resources (npj Comput Mater. 2019, 5, 78). Therefore, there is an urgent need to develop non-metal catalysts with low cost, high activity, and high selectivity to achieve efficient H2O2 production. Summary of the Invention

[0005] The object of the present invention is to provide a preparation method and application of an N / O co-doped porous interconnected hollow carbon sphere catalyst. Innovatively, guanine and tetraethyl orthosilicate (TEOS) are used as a novel bifunctional template. Through the strategies of molecular self-assembly and synergistic etching, the synergistic effect of the two in the carbon sphere structure regulation is realized for the first time: guanine serves as the nitrogen / oxygen source and carbon precursor, while TEOS generates a silica framework through hydrolysis and regulates the pore distribution. Finally, a regular hollow sphere interconnected network is formed through carbonization and etching. The prepared material not only has a perfect hollow sphere structure, but also exhibits excellent catalytic activity (the H2O2 selectivity is as high as 94.3%) and stability (both the current and selectivity can be stabilized for more than 10 h) in the 2e - ORR.

[0006] To achieve the above object, the present invention adopts the following technical solutions: A preparation method of an N / O co-doped porous interconnected hollow carbon sphere catalyst, comprising the following steps: (1) Mix ammonia water, ethanol and deionized water evenly, then add tetraethyl orthosilicate (TEOS), and stir vigorously to mix evenly. Subsequently, the SiO2 nanosphere template agent obtained by centrifugation, drying and grinding; (2) Ultrasonically disperse the SiO2 nanosphere template agent obtained in step (1) in deionized water to form a uniform suspension, then add guanine and ammonia water to the suspension, and continuously stir. After the obtained suspension is centrifuged, dried and ground, a pure white powder precursor is obtained; (3) Heat and keep the precursor obtained in step (2) under a protective gas atmosphere, and naturally cool to room temperature after the reaction ends to obtain a gray powder; (4) Immerse the gray powder obtained in step (3) in a NaOH solution, heat it in an oil bath and keep it warm for etching, then filter and wash it with deionized water. The obtained residue is freeze-dried and ground to finally obtain an N / O co-doped porous interconnected hollow carbon sphere catalyst.

[0007] Further, in step (1), the volume ratio of TEOS, ammonia water, ethanol and deionized water is 1:3:50:1.

[0008] Further, in step (2), the stirring time is 48 h and the centrifugation speed is 8000 rpm.

[0009] Further, in step (1), the dosage ratio of the SiO2 nanosphere template agent, guanine, ammonia water and deionized water is 1.8 g:1.6 g:21 mL:220 mL.

[0010] Furthermore, the stirring time in step (2) is 48 h, the centrifugation speed is 8000 rpm, and the ultrasonic time is 30 min.

[0011] Furthermore, the protective gas in step (3) is nitrogen, and the heating rate is 5 o °C / min, and the heat preservation temperature is 600 o °C - 900 o °C, and the heat preservation time is 2 h.

[0012] Furthermore, the concentration of the NaOH solution in step (4) is 2 mol / L.

[0013] Furthermore, the temperature of the oil bath in step (4) is 80 o °C, and the etching time is 6 h.

[0014] An N / O co-doped porous interconnected hollow carbon sphere catalyst obtained by the above preparation method and its application in the 2e - ORR to generate H2O2.

[0015] Compared with the prior art, the advantages of the present invention are as follows: (1) Using guanine as the raw material and silica as the template, an environmentally friendly carbon material is synthesized through hydrogen bond self-assembly, high-temperature pyrolysis, and etching. The obtained material has a unique structure of porous interconnected hollow nanospheres, and the thickness of the spherical shell and the heteroatom doping amount can be precisely designed. When this material is used in the 2e - ORR, the selectivity of H2O2 can reach up to 94.3%, and the stability can reach more than 10 h.

[0016] (2) Biomass small molecule guanine is a nitrogen-rich small molecule containing C, N, and O elements simultaneously. Therefore, the carbon material prepared with it as the raw material has the characteristic of high nitrogen content; and during the synthesis process, nitrogen atoms and oxygen atoms can be introduced in situ without additional dopants, so it is easy to obtain an N / O co-doped carbon material, thereby regulating the electronic structure and activity of the carbon material. At the same time, the carbon material derived from guanine molecules has a rich pore structure, which is conducive to providing more internal active sites during the ORR process and promoting rapid electron transfer, shortening the diffusion path of reactants / products. Using silica as the template sacrificial agent can customize the unique structure of the material and help improve the specific surface area and the density of reaction active sites of the material. In addition, guanine is not only low-cost and renewable, but also widely exists in biological wastes. Converting it into a high-value-added electrocatalyst is conducive to promoting resource recovery and carbon fixation processes, and is suitable for large-scale industrial preparation of nanocarbon materials. Description of the Drawings

[0017] Figure 1Synthesis schematic diagram for preparing the N / O co-doped porous interconnected hollow carbon sphere catalyst of the present invention.

[0018] Figure 2 Scanning electron microscopy (SEM) image of the hollow sphere carbon material obtained in Example 1.

[0019] Figure 3 Transmission electron microscopy (TEM) image of the hollow sphere carbon material obtained in Example 1.

[0020] Figure 4 XPS spectra of the hollow sphere carbon materials obtained in Examples 1-4.

[0021] Figure 5 XPS N 1s spectra of the hollow sphere carbon materials obtained in Examples 1-4.

[0022] Figure 6 XPS O 1s spectra of the hollow sphere carbon materials obtained in Examples 1-4.

[0023] Figure 7 Performance graph of the hollow sphere carbon materials obtained in Examples 1-4 in 2e - ORR.

[0024] Figure 8 Stability graph of the hollow sphere carbon material obtained in Example 1 in 2e - ORR.

[0025] Figure 9 SEM image of the hollow sphere carbon material obtained in Example 1 after stability test.

[0026] Figure 10 TEM image of the hollow sphere carbon material obtained in Example 1 after stability test.

[0027] Figure 11 SEM image of the carbon material obtained in Comparative Example 1.

[0028] Figure 12 SEM image of the carbon material obtained in Comparative Example 2.

[0029] Figure 13 Performance graph of the carbon materials obtained in Example 1 and Comparative Examples 1 and 2 in 2e - ORR. Detailed implementation manners

[0030] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments.

[0031] Example 1 HCS-600 (1)Measure 21 mL of ammonia water, 350 mL of ethanol, and 7 mL of deionized water separately, mix them evenly in a beaker, add 7 mL of tetraethyl orthosilicate (TEOS), place it on a magnetic stirrer, stir at 500 rpm for 7 h, then centrifuge at 8000 rpm, and place the separated precipitate in a 60 o °C oven and dry for 12 h, then grind to obtain the original SiO2 nanospheres; (2)Disperse 1.8 g of the obtained SiO2 nanospheres in 220 mL of deionized water and ultrasonically treat for 30 min to form a uniform suspension. Then weigh 1.6 g of guanine and measure 21 mL of ammonia water separately, add them to the above suspension, place it on a magnetic stirrer, and continuously stir at 500 rpm for 48 h. Centrifuge the obtained suspension at 8000 rpm and dry it in a 60 o °C oven for 24 h, and obtain a white powder precursor after grinding; (3)Carry out carbonization treatment on the precursor obtained in step (2) under a N2 atmosphere, set the heating rate to 5 o °C / min, raise the temperature from 30 o °C to 600 o °C and keep it for 2 h, naturally cool to room temperature, and obtain a gray powder precursor after grinding, which is named SiO2@GUA-600 precursor; (4)Immerse the SiO2@GUA-600 precursor in a 2 mol / L NaOH aqueous solution and etch it in an 80 o °C oil bath for 6 h. Then, wash and filter with deionized water to remove the residual NaOH, and freeze-dry the obtained residue for 24 h. After grinding, the N / O co-doped porous interconnected hollow carbon sphere catalyst can be obtained, which is named HCS-600.

[0032] Example 2 HCS-700 (1)Measure 21 mL of ammonia water, 350 mL of ethanol, and 7 mL of deionized water separately, mix them evenly in a beaker, add 7 mL of TEOS, place it on a magnetic stirrer, stir at 500 rpm for 7 h, then centrifuge at 8000 rpm, and place the separated precipitate in a 60 o °C oven and dry for 12 h, then grind to obtain the original SiO2 nanospheres; (2)Disperse 1.8 g of the obtained SiO2 nanospheres in 220 mL of deionized water and ultrasonically treat for 30 min to form a uniform suspension. Then weigh 1.6 g of guanine and measure 21 mL of ammonia water separately, add them to the above suspension, place it on a magnetic stirrer, and continuously stir at 500 rpm for 48 h. Centrifuge the obtained suspension at 8000 rpm and dry it in a 60 oThe C oven was dried for 24 h, and a white powder precursor was obtained after grinding; (3)The precursor obtained in step (2) was carbonized under an N2 atmosphere, and the heating rate was set at 5 o C / min, and the temperature was raised from 30 o C to 700 o C and held for 2 h, then naturally cooled to room temperature, and a gray powder precursor was obtained after grinding, which was named SiO2@GUA-700 precursor; (4)The SiO2@GUA-600 precursor was immersed in a 2 mol / L NaOH aqueous solution and etched at 80 o C in an oil bath for 6 h. Then, it was washed with deionized water and filtered to remove the residual NaOH, and the obtained residue was freeze-dried for 24 h. After grinding, the N / O co-doped porous interconnected hollow carbon sphere catalyst, named HCS-700, was obtained.

[0033] Example 3 HCS-800 (1)21 mL of ammonia water, 350 mL of ethanol and 7 mL of deionized water were respectively measured and mixed evenly in a beaker, then 7 mL of TEOS was added and placed on a magnetic stirrer and stirred at 500 rpm for 7 h. Subsequently, it was centrifuged at 8000 rpm, and the separated precipitate was placed in a 60 o C oven and dried for 12 h, and then ground to obtain the original SiO2 nanospheres; (2)1.8 g of the obtained SiO2 nanospheres were dispersed in 220 mL of deionized water and ultrasonicated for 30 min to form a homogeneous suspension. Then, 1.6 g of guanine and 21 ml of ammonia water were respectively weighed and added to the above suspension, and it was continuously stirred at 500 rpm on a magnetic stirrer for 48 h. The obtained suspension was centrifuged at 8000 rpm and dried in a 60 o C oven for 24 h, and a white powder precursor was obtained after grinding; (3)The precursor obtained in step (2) was carbonized under an N2 atmosphere, and the heating rate was set at 5 o C / min, and the temperature was raised from 30 o C to 800 o C and held for 2 h, then naturally cooled to room temperature, and a gray powder precursor was obtained after grinding, which was named SiO2@GUA-800 precursor; (4)The SiO2@GUA-600 precursor was immersed in a 2 mol / L NaOH aqueous solution and at 80 oEtch for 6 h under the condition of C oil bath heat preservation. After that, wash and filter with deionized water to remove the residual NaOH, and freeze-dry the obtained residue for 24 h. After grinding, the N / O co-doped porous interconnected hollow carbon sphere catalyst can be obtained, named HCS-800.

[0034] Example 4 HCS-900 (1) Measure 21 mL of ammonia water, 350 mL of ethanol and 7 mL of deionized water respectively, mix them evenly in a beaker, add 7 mL of TEOS, place it on a magnetic stirrer and stir at a speed of 500 rpm for 7 h. Then centrifuge at a speed of 8000 rpm, and place the separated precipitate in 60 o Dry in an oven at C for 12 h and then grind to obtain the original SiO2 nanospheres; (2) Disperse the obtained 1.8 g of SiO2 nanospheres in 220 mL of deionized water and ultrasonically treat for 30 min to form a uniform suspension. Then weigh 1.6 g of guanine and measure 21 mL of ammonia water respectively, add them to the above suspension, place it on a magnetic stirrer and continuously stir at a speed of 500 rpm for 48 h. Centrifuge the obtained suspension at a speed of 8000 rpm and dry in an oven at 60 o Dry in an oven at C for 24 h, and obtain a white powder precursor after grinding; (3) Carbonize the precursor obtained in step (2) under a N2 atmosphere, set the heating rate to 5 o C / min, raise the temperature from 30 o C to 900 o C and keep it warm for 2 h, then naturally cool to room temperature, and obtain a gray powder precursor after grinding, named SiO2@GUA-900 precursor; (4) Immerse the SiO2@G-600 precursor in a NaOH solution with a concentration of 2 mol / L, and etch it under the condition of 80 o C oil bath heat preservation for 6 h. After that, wash and filter with deionized water to remove the residual NaOH, and freeze-dry the obtained residue for 24 h. After grinding, the N / O co-doped porous interconnected hollow carbon sphere catalyst can be obtained, named HCS-900.

[0035] Comparative Example 1 NC2-600 (1) Measure 21 mL of ammonia water, 350 mL of ethanol and 7 mL of deionized water respectively, mix them evenly in a beaker, add 7 mL of TEOS, place it on a magnetic stirrer and stir at a speed of 500 rpm for 7 h. Then centrifuge at a speed of 8000 rpm, and place the separated precipitate in 60 o Dry in an oven at C for 12 h and then grind to obtain the original SiO2 nanospheres; (2) Disperse the obtained 3.2 g of SiO2 nanospheres in 220 mL of deionized water and ultrasonically treat for 30 min to form a uniform suspension. Then, weigh 1.6 g of guanine and measure 21 mL of ammonia water respectively, add them into the above suspension, place it on a magnetic stirrer and stir continuously at a speed of 500 rpm for 48 h. Centrifuge the obtained suspension at a speed of 8000 rpm and dry it in an oven at 60 o C for 24 h, and obtain a white powder precursor after grinding; (3) Carbonize the precursor obtained in step (2) under a N2 atmosphere, set the heating rate to 5 o C / min, raise the temperature from 30 o C to 600 o C and keep it warm for 2 h, then cool it naturally to room temperature, and obtain a gray powder precursor after grinding, which is named SiO2@GUA2-600 precursor; (4) Immerse the SiO2@G-600 precursor in a NaOH solution with a concentration of 2 mol / L, and etch it in an oil bath at 80 o C for 6 h. Then, wash it with deionized water and filter to remove the residual NaOH, and freeze-dry the obtained residue for 24 h. After grinding, the N / O co-doped porous three-dimensional carbon framework catalyst can be obtained, which is named NC2-600.

[0036] Comparative Example 2 NC 0.4 -600 (1) Measure 21 mL of ammonia water, 350 mL of ethanol and 7 mL of deionized water respectively, mix them evenly in a beaker, add 7 mL of TEOS, place it on a magnetic stirrer and stir at a speed of 500 rpm for 7 h. Then, centrifuge at a speed of 8000 rpm, and place the separated precipitate in an oven at 60 o C and dry it for 12 h, and then grind it to obtain the original SiO2 nanospheres; (2) Disperse the obtained 0.64 g of SiO2 nanospheres in 220 mL of deionized water and ultrasonically treat for 30 min to form a uniform suspension. Then, weigh 1.6 g of guanine and measure 21 mL of ammonia water respectively, add them into the above suspension, place it on a magnetic stirrer and stir continuously at a speed of 500 rpm for 48 h. Centrifuge the obtained suspension at a speed of 8000 rpm and dry it in an oven at 60 o C for 24 h, and obtain a white powder precursor after grinding; (3) Carbonize the precursor obtained in step (2) under a N2 atmosphere, set the heating rate to 5 o C / min, raise the temperature from 30 o C to 600 oAdd C and keep warm for 2 h, then cool naturally to room temperature. After grinding, a gray powder precursor is obtained, which is named SiO2@GUA 0.4 -600 precursor; (4)Immerse the SiO2@G-600 precursor in a NaOH solution with a concentration of 2 mol / L and etch it in an 80 o C oil bath for 6 h. Then, wash and filter with deionized water to remove the residual NaOH, and freeze-dry the obtained residue for 24 h. After grinding, the N / O co-doped two-dimensional sheet / sphere composite catalyst, named NC 0.4 -600, can be obtained.

[0037] Figure 1 This is the synthesis schematic diagram of the N / O co-doped porous interconnected hollow carbon sphere catalyst prepared by the present invention.

[0038] Figure 2 This is the SEM image of HCS-600 prepared in Example 1. It can be seen from the figure that HCS-600 presents a three-dimensional porous interconnected hollow sphere structure.

[0039] Figure 3 This is the TEM image of HCS-600 prepared in Example 1. The result is consistent with that of SEM, further confirming the three-dimensional hollow sphere structure of HCS-600.

[0040] Figure 4 This is the XPS spectrum of the porous interconnected hollow carbon sphere catalysts synthesized in Examples 1-4. It can be seen from the figure that all samples are composed of C, N, and O elements.

[0041] Figure 5 This is the XPS N 1s spectrum of the porous interconnected hollow carbon sphere catalysts synthesized in Examples 1-4. It can be seen from the figure that the N 1s spectrum can be deconvoluted into four peaks, corresponding to pyridine nitrogen, pyrrole nitrogen, graphitic nitrogen, and nitrogen oxide species respectively. It is also observed that the binding energies of pyridine nitrogen and pyrrole nitrogen shift to lower values, indicating that nitrogen species are successfully introduced and the electronic structure of the carbon skeleton is controllably adjusted.

[0042] Figure 6 This is the XPS O 1s spectrum of the porous interconnected hollow carbon sphere catalysts synthesized in Examples 1-4. It can be seen from the figure that the O 1s spectrum can be deconvoluted into three peaks, corresponding to C=O, HO-C=O, and C-OH respectively. In addition, it is also observed that C=O and HO-C=O also show a shift to higher binding energies, which fully indicates that oxygen species participate in regulating the electronic structure of the carbon skeleton while being introduced.

[0043] Figure 11SEM image of the carbon material obtained in Comparative Example 1. As can be seen from the figure, when the ratio of SiO2 template to guanine is too large (the ratio of SiO2 to guanine is 2), the obtained carbon material is not a porous interconnected hollow sphere structure, but a porous three-dimensional carbon skeleton morphology.

[0044] Figure 12 SEM image of the carbon material obtained in Comparative Example 2. As can be seen from the figure, when the amount of SiO2 template is insufficient (the ratio of SiO2 to guanine is 0.4), the obtained carbon material is not a porous interconnected hollow sphere structure, but a composite morphology of a small amount of spheres embedded in flakes.

[0045] Table 1 shows the C, N, O element contents of the catalysts synthesized from the porous interconnected hollow carbon spheres in Examples 1-4, as well as the contents of different elemental species functional groups. As can be seen from Table 1, with the increase of pyrolysis temperature, the contents of pyridine nitrogen and pyrrole nitrogen decrease, and the change of pyridine nitrogen is the most significant, decreasing from 17.42% to 3.78%. On the contrary, the content of graphitic nitrogen increases with the increase of temperature, indicating that pyridine nitrogen and pyrrole nitrogen dominate in the samples pyrolyzed at lower temperatures, while with the increase of carbonization temperature, the main form of nitrogen species gradually changes to graphitic nitrogen; in addition, the content of HO-C=O also shows a slight decrease with the increase of pyrolysis temperature.

[0046] Table 1 Elemental analysis table of the materials synthesized in Examples 1-4 The materials synthesized in Examples 1-4 were used for 2e - ORR to prepare H2O2. The specific experimental measurement method is as follows: The electrochemical performance was tested by a rotating disk-ring electrode (RRDE) system to evaluate the selectivity of H2O2. In this system, a disk electrode with an area of 0.1256 cm 2 was used as the working electrode, a Pt ring electrode with an area of 0.1884 cm 2 , a mercury / mercuric oxide electrode (Hg / HgO) as the reference electrode, and a platinum sheet as the counter electrode. All the test experiments were carried out at room temperature in an O2-saturated 0.1 M KOH electrolyte solution. To prepare the catalyst layer, 2.5 mg of the catalyst was added to 0.55 mL of Nafion dispersion (the dispersion was prepared by mixing deionized water, ethanol, and Nafion (5 wt%) in a volume ratio of 5:25:2). Subsequently, this mixture was ultrasonically treated for 0.5 hours to ensure uniform dispersion of the catalyst, forming an ink-like suspension. Then, 9 μL of this catalyst ink was drop-coated on the pre-polished disk electrode and allowed to dry. The loading of all catalysts was standardized to 0.33 mg / cm². The experimental results are as Figure 7As shown, the HCS-600 with the highest nitrogen content exhibits a H2O2 selectivity as high as 94.3%, and there is an obvious downward trend in H2O2 selectivity with the increase of pyrolysis temperature. Figure 13 It is a performance graph of catalysts synthesized with different raw material ratios at the same temperature. As can be seen from the graph, the H2O2 selectivity of the HCS-600 catalyst is significantly better than that of the NC2-600 and NC 0.4 -600 catalysts. Figure 8 It is a stability test of HCS-600 by RRDE technology. The results show that there is no obvious change in H2O2 selectivity during the 10 h stability test. Figure 9 、 10 They are the SEM and TEM of HCS-600 after the stability test respectively. As can be seen from the graph, HCS-600 still maintains the original three-dimensional porous interconnected hollow sphere structure, indicating that HCS-600 has excellent structural stability during the test.

[0047] The above are only the preferred embodiments of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope covered by the present invention.

Claims

1. A method for preparing a N / O co-doped porous interconnected hollow carbon sphere catalyst, characterized in that: The following steps are involved: (1) After ammonia water, ethanol and deionized water are mixed evenly, tetraethyl orthosilicate is added, and the mixture is stirred and mixed evenly, followed by centrifugation, drying and grinding to obtain a SiO2 nanosphere template; (2) ultrasonically dispersing the SiO2 nanosphere template obtained in step (1) in deionized water to form a uniform suspension, then adding guanine and ammonia water, stirring continuously, and centrifuging, drying and grinding the obtained suspension to obtain a pure white powder precursor; (3) heating and keeping the precursor obtained in step (2) under a protective gas atmosphere, and naturally cooling to room temperature after the reaction is completed to obtain a gray powder; (4) The gray powder obtained in step (3) is immersed in a NaOH solution, heated in an oil bath and kept warm for etching, and then filtered and washed with deionized water. The residue is freeze-dried and ground to finally obtain a N / O co-doped porous interconnected hollow carbon sphere catalyst.

2. The method for preparing the N / O co-doped porous interconnected hollow carbon sphere catalyst according to claim 1, characterized in that: The volume ratio of tetraethyl orthosilicate, ammonia water, ethanol and deionized water in step (1) is 1:3:50:

1.

3. The method for preparing the N / O co-doped porous interconnected hollow carbon sphere catalyst according to claim 1, characterized in that: The stirring time in step (1) is 7 h, the stirring speed is 500 rpm, and the centrifugal speed is 8000 rpm.

4. The method for preparing the N / O co-doped porous interconnected hollow carbon sphere catalyst according to claim 1, characterized in that: The dosage ratio of the SiO2 nanosphere template, guanine, ammonia water and deionized water in step (2) is 1.8 g: 1.6 g: 21 mL: 220 mL.

5. The method for preparing the N / O co-doped porous interconnected hollow carbon sphere catalyst according to claim 1, characterized in that: The stirring time in step (2) is 48 h, the centrifugal speed is 8000 rpm, and the ultrasonic time is 30 min.

6. The method for preparing the N / O co-doped porous interconnected hollow carbon sphere catalyst according to claim 1, characterized in that: In step (3), the protective gas is nitrogen, and the heating rate is 5 o C / min, holding temperature is 600 o C-900 o C, the holding time is 2 h.

7. The method for preparing the N / O co-doped porous interconnected hollow carbon sphere catalyst according to claim 1, characterized in that: The concentration of the NaOH solution in step (4) is 2 mol / L.

8. The method for preparing the N / O co-doped porous interconnected hollow carbon sphere catalyst according to claim 1, characterized in that: The temperature of the oil bath in step (4) is 80 o C, the etching time is 6 h.

9. The N / O co-doped porous interconnected hollow carbon sphere catalyst obtained by the preparation method according to any one of claims 1 to 8.

10. Use of the N / O co-doped porous interconnected hollow carbon sphere catalyst as claimed in claim 9 in the electrochemical oxygen reduction to prepare hydrogen peroxide.

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