Nitrogen-doped nanocarbon cages and their preparation method and application

Abstract

The present invention relates to the technical field of novel nano-carbon materials, and discloses a nitrogen-doped nano-carbon cage and a preparation method thereof, as well as the application of the nitrogen-doped nano-carbon cage in a fuel cell catalyst support and / or a fuel cell catalyst, wherein the nitrogen-doped nano-carbon cage has a hollow cage-like structure and a diameter of 2-200 nm; based on the total molar amount of nitrogen, the molar content of pyrrolic nitrogen and / or pyridinic nitrogen in the nitrogen on the surface of the nitrogen-doped nano-carbon cage measured by X-ray photoelectron spectroscopy is greater than 80%. When the nitrogen-doped nano-carbon cage is applied to a fuel cell catalyst support and / or a fuel cell catalyst, it exhibits good catalytic activity.

Description

Technical Field

[0001] The present invention relates to the technical field of novel nanocarbon materials, and in particular to nitrogen-doped nanocarbon cages and a preparation method thereof, as well as application of the nitrogen-doped nanocarbon cages in fuel cell catalyst supports and / or fuel cell catalysts. Background Art

[0002] In recent years, research in carbon nanotechnology has been quite active, and a variety of new nanographitic carbon materials have been developed, such as graphitic carbon nanocups, nanohorns, nanorings, and nanocages. The emergence of these materials has enriched the structure of nanographitic carbon materials, opening up a wider range of applications. Among them, graphene nanocages are a very unique new nanographitic structure with a unique hollow structure similar to fullerenes and a relatively controllable nanometer size. This unique hollow porous nanographitic structure can endow the material with a series of unique physical and chemical properties, and is expected to be applied in many fields such as industrial catalysis, electrochemical energy storage, drug delivery, and optical devices.

[0003] To enhance the performance of nanocarbon materials and adapt them to various applications, researchers often introduce heteroatoms (such as oxygen and nitrogen atoms) into nanocarbon materials to improve their application properties. When introducing nitrogen atoms into nanocarbon materials, they are generally divided into chemical nitrogen and structural nitrogen based on their chemical environment. Chemical nitrogen primarily appears on the material surface as surface functional groups, such as amino or nitrosyl groups. Structural nitrogen primarily refers to nitrogen atoms that enter the nanocarbon material's backbone and bond to carbon atoms, primarily including graphitic nitrogen, pyridinic nitrogen, and pyrrolic nitrogen. Different types of nitrogen atoms exhibit different properties. The paper Carbon 115 (2017) 763-772 describes the effects of different nitrogen species on the oxygen reduction reaction (ORR) activity of Pt / C catalysts. The order of nitrogen species that enhance activity is pyridinic nitrogen > pyrrolic nitrogen > graphitic nitrogen > quaternary ammonium nitrogen > oxidized nitrogen > pristine carbon material. However, obtaining nanocarbon materials containing only a single nitrogen species is difficult. Therefore, although much progress has been made in the research on the doping, modification and performance of nanocarbon materials, there is still no consensus on some basic issues, and in-depth research is still needed on doped and modified nanocarbon materials, their preparation methods and catalytic properties. Summary of the Invention

[0004] To overcome the aforementioned problems of the prior art, the present invention provides a nitrogen-doped nanocarbon cage, a method for preparing the same, and the use of the nitrogen-doped nanocarbon cage in a fuel cell catalyst support and / or fuel cell catalyst. The nitrogen-doped nanocarbon cage provided by the present invention has a molar content of pyrrolic and / or pyridinic nitrogen greater than 80% of the nitrogen on the surface of the nitrogen-doped nanocarbon cage, as measured by X-ray photoelectron spectroscopy, based on the total molar amount of nitrogen.

[0005] In order to achieve the above-mentioned object, the first aspect of the present invention provides a nitrogen-doped nanocarbon cage, wherein the nitrogen-doped nanocarbon cage has a hollow cage-like structure and a diameter of 2-200 nm; based on the total molar amount of nitrogen, the molar content of pyrrolic nitrogen and / or pyridinic nitrogen in the nitrogen on the surface of the nitrogen-doped nanocarbon cage measured by X-ray photoelectron spectroscopy is greater than 80%.

[0006] A second aspect of the present invention provides a method for preparing nitrogen-doped nanocarbon cages, the method comprising the following steps:

[0007] (1) providing a solution containing a transition metal salt, a nitrogen-containing organic carboxylic acid, and a solvent, and then drying to obtain a precursor, wherein the nitrogen-containing organic carboxylic acid is ethylenediaminetetraacetic acid; and the molar ratio of the transition metal salt to the nitrogen-containing organic carboxylic acid, calculated as the transition metal element, is 1:0.5-1;

[0008] (2) pyrolyzing the precursor obtained in step (1) at a temperature of 850-1000° C. under an inert atmosphere or a reducing atmosphere to obtain a pyrolysis product;

[0009] (3) The pyrolysis product is acid-washed, and then solid-liquid separated, washed and dried.

[0010] The third aspect of the present invention provides a nitrogen-doped nanocarbon cage prepared by the preparation method described in the second aspect.

[0011] A fourth aspect of the present invention provides a use of the nitrogen-doped nanocarbon cage as described in the first aspect or the third aspect in a fuel cell catalyst support and / or a fuel cell catalyst.

[0012] Through the above technical solution, the present invention has the following advantages:

[0013] (1) The nitrogen-doped nanocarbon cages provided by the present invention have a hollow cage-like structure with a diameter of 2-200 nm. The molar content of pyrrolic nitrogen and / or pyridinic nitrogen in the nitrogen on the surface of the nitrogen-doped nanocarbon cages is greater than 80% as measured by X-ray photoelectron spectroscopy, based on the total molar amount of nitrogen. The nitrogen-doped nanocarbon cages provided by the present invention exhibit good catalytic activity when used in fuel cell catalyst supports and / or fuel cell catalysts.

[0014] (2) The preparation method provided by the present invention uses a specific nitrogen-containing organic carboxylic acid and controls the specific ratio of the transition metal salt to the specific nitrogen-containing organic carboxylic acid, so that the nitrogen on the surface of the prepared nitrogen-doped nanocarbon cage exists in the form of pyrrole nitrogen or pyrrole nitrogen and pyridinic nitrogen, which is beneficial to improving the oxygen reduction reaction (ORR) activity of the fuel cell catalyst (Pt / C catalyst). BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a TEM image of the nitrogen-doped nanocarbon cage prepared in Example 1;

[0016] Figure 2 is the XPS graph of the nitrogen-doped nanocarbon cage prepared in Example 1;

[0017] Figure 3 This is the N1s peak spectrum of the XPS of the nitrogen-doped nanocarbon cage prepared in Example 1;

[0018] Figure 4 is the BJH pore size distribution curve of the nitrogen-doped nanocarbon cage prepared in Example 1;

[0019] Figure 5 This is the N1s peak spectrum of the XPS of the nitrogen-doped nanocarbon cage prepared in Example 2;

[0020] Figure 6 This is the N1s peak spectrum of the XPS of the nitrogen-doped nanocarbon cage prepared in Example 3;

[0021] Figure 7 This is the N1s peak spectrum of the XPS of the nitrogen-doped nanocarbon cage prepared in Example 4;

[0022] Figure 8 This is the N1s peak spectrum of the XPS of the nitrogen-doped nanocarbon cage prepared in Comparative Example 1;

[0023] Figure 9 This is the N1s peak spectrum of the XPS of the nitrogen-doped nanocarbon cage prepared in Comparative Example 2;

[0024] Figure 10 This is the N1s peak spectrum of the XPS of the nitrogen-doped nanocarbon cage prepared in Comparative Example 3;

[0025] Figure 11 This is the N1s peak spectrum of the XPS of the nitrogen-doped nanocarbon cage prepared in Comparative Example 4. DETAILED DESCRIPTION

[0026] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0027] A first aspect of the present invention provides a nitrogen-doped nanocarbon cage, wherein the nitrogen-doped nanocarbon cage has a hollow cage-like structure and a diameter of 2-200 nm; based on the total molar amount of nitrogen, the molar content of pyrrolic nitrogen and / or pyridinic nitrogen in the nitrogen on the surface of the nitrogen-doped nanocarbon cage measured by X-ray photoelectron spectroscopy is greater than 80%.

[0028] In the present invention, the hollow cage-like shape has a conventional definition in the art, specifically referring to a hollow sphere or spherical-like shape surrounded by a graphitized carbon layer.

[0029] According to some embodiments of the present invention, the diameter of the nitrogen-doped nanocarbon cage is 2-200 nm, preferably 2-100 nm, more preferably 5-50 nm, and even more preferably 5-20 nm.

[0030] In the present invention, the surface morphology of the material was characterized by high-resolution transmission electron microscopy (HRTEM). The HRTEM used was a JEM-2100 (JEOL Ltd.) at an accelerating voltage of 200 kV. The diameter of the nitrogen-doped nanocarbon cages can be measured using HRTEM images.

[0031] In the present invention, the terms "pyrrolic nitrogen", "pyridinic nitrogen", "graphitic nitrogen" and "oxidized nitrogen" have the conventional meanings in the art, specifically referring to: pyridinic nitrogen is a nitrogen species identified by a characteristic peak corresponding to a binding energy of 398.7-399.1 eV in the X-ray photoelectron spectrum; pyrrolic nitrogen is a nitrogen species identified by a characteristic peak corresponding to a binding energy of 398.8-400.2 eV in the X-ray photoelectron spectrum; graphitic nitrogen is a nitrogen species identified by a characteristic peak corresponding to a binding energy of 401.2-409.8 eV in the X-ray photoelectron spectrum; and oxidized nitrogen is a nitrogen species identified by a characteristic peak corresponding to a binding energy of 402.8-403.6 eV in the X-ray photoelectron spectrum.

[0032] In the present invention, X-ray photoelectron spectroscopy was performed on an ESCALab250 X-ray photoelectron spectrometer equipped with ThermoAvantage V5.926 software from Thermo Scientific. The excitation source was monochromatic AlKα X-ray with an energy of 1486.6 eV and a power of 150 W. The penetration energy used in the narrow scan was 30 eV. The basic vacuum during the analysis was 6.53 × 10 -9 The electron binding energy was calibrated using the C1s peak of elemental carbon (284.6 eV). Data were processed using Thermo Avantage software, and the sensitivity factor method was used for quantitative analysis in the analysis module.

[0033] In the present invention, the "nitrogen" in the term "nitrogen-doped nanocarbon cage" refers to the nitrogen element, and specifically refers to the nitrogen element in various forms formed in the nitrogen-doped nanocarbon cage during the preparation process of the nitrogen-doped nanocarbon cage.

[0034] According to some embodiments of the present invention, based on the total molar amount of nitrogen, the molar content of pyrrolic nitrogen and / or pyridinic nitrogen in the nitrogen on the surface of the nitrogen-doped nanocarbon cage measured by X-ray photoelectron spectroscopy is greater than 80%, preferably greater than 90%.

[0035] According to some embodiments of the present invention, preferably, the molar ratio of pyrrolic nitrogen to pyridinic nitrogen in the nitrogen on the surface of the nitrogen-doped nanocarbon cage measured by X-ray photoelectron spectroscopy is greater than 2, preferably greater than 3.

[0036] According to some embodiments of the present invention, preferably, the molar content of pyrrolic nitrogen in the nitrogen on the surface of the nitrogen-doped nanocarbon cage measured by X-ray photoelectron spectroscopy is 85.8-100%, and the molar content of pyridinic nitrogen is 0-14.2%, more preferably, the molar content of pyrrolic nitrogen is 100%.

[0037] The nitrogen on the surface of the nitrogen-doped nanocarbon cage provided by the present invention exists in the form of pyrrolic nitrogen and pyridinic nitrogen, which is beneficial to improving the oxygen reduction reaction (ORR) activity of the fuel cell catalyst (Pt / C catalyst).

[0038] According to some embodiments of the present invention, preferably, the nitrogen-doped nanocarbon cage may further contain oxygen, which may be oxygen in various forms formed in the nitrogen-doped nanocarbon cage during the preparation process of the nitrogen-doped nanocarbon cage.

[0039] According to some embodiments of the present invention, preferably, the molar content of carbon on the surface of the nitrogen-doped nanocarbon cage measured by X-ray photoelectron spectroscopy is 89-92%, the molar content of nitrogen is 1-3%, and the molar content of oxygen is 5-10%.

[0040] According to some embodiments of the present invention, the nitrogen-doped nanocarbon cage may contain doping elements that are known to those skilled in the art and can be applied to carbon materials. Preferably, the nitrogen-doped nanocarbon cage does not contain elements such as nickel, sulfur, boron, phosphorus, fluorine, chlorine, bromine, and iodine.

[0041] According to some embodiments of the present invention, preferably, the nitrogen-doped nanocarbon cage has a dual mesopore distribution peak, and the dual mesopore distribution peak corresponds to the first most probable pore diameter and the second most probable pore diameter, respectively, the first most probable pore diameter is 3.5-4 nanometers, and the second most probable pore diameter is 6-9.5 nanometers. In this preferred embodiment, the small pore size can further provide a large specific surface area for the material, increase the active sites, and the large pore size can provide a diffusion channel for molecules or ions, accelerate the mass transfer rate and provide higher stability.

[0042] According to some embodiments of the present invention, preferably, the BET specific surface area of ​​the nitrogen-doped nanocarbon cage is greater than 300 m 2 / g, with a total pore volume greater than 0.6 cm 3 / g.

[0043] More preferably, the BET specific surface area of ​​the nitrogen-doped nanocarbon cage is greater than 460 m 2 / g, with a total pore volume greater than 0.7 cm 3 The nitrogen-doped nanocarbon cage has a rich pore structure and a large specific surface area.

[0044] In the present invention, the term "mesopore" is defined as a pore with a pore diameter in the range of 2-50 nm.

[0045] In the present invention, the pore structure properties of nitrogen-doped nanocarbon cages were determined using the BET test method. Specifically, a Quantachrome AS-6B analyzer was used for measurement. The BET specific surface area and pore volume of the nitrogen-doped nanocarbon cages were obtained using the Brunauer-Emmett-Taller (BET) method, and the mesopore distribution curve was calculated from the desorption curve using the Barrett-Joyner-Halenda (BJH) method.

[0046] According to some embodiments of the present invention, preferably, in the Raman curve of the nitrogen-doped nanocarbon cage, I D / I G The range of is 0.2-1, preferably 0.3-0.8. The nitrogen-doped nanocarbon cage of the present invention has obvious D peak and G peak, and has a certain degree of graphitization.

[0047] In the present invention, the graphitization degree of nitrogen-doped nanocarbon cages was characterized by Raman spectroscopy, 1355 cm -1 The peak at 1585 cm (D peak) is attributed to structural defects and is amorphous carbon. -1 The peak (G peak) is attributed to the carbon in the planar structure. Usually I D / I G (D peak and G peak intensity ratio) to characterize the degree of graphitization of the material. D / IG The higher the value, the more defects there are and the lower the degree of graphitization. The Raman spectrum of the material was obtained using a RM2000 micro-confocal Raman spectrometer (product of Reinshaw Company). Technical specifications: The excitation source used was a He-Ne laser with a wavelength of 525 nm.

[0048] A second aspect of the present invention provides a method for preparing nitrogen-doped nanocarbon cages, the method comprising the following steps:

[0049] (1) providing a solution containing a transition metal salt, a nitrogen-containing organic carboxylic acid, and a solvent, and then drying to obtain a precursor, wherein the nitrogen-containing organic carboxylic acid is ethylenediaminetetraacetic acid; and the molar ratio of the transition metal salt to the nitrogen-containing organic carboxylic acid, calculated as the transition metal element, is 1:0.5-1;

[0050] (2) pyrolyzing the precursor obtained in step (1) at a temperature of 850-1000° C. under an inert atmosphere or a reducing atmosphere to obtain a pyrolysis product;

[0051] (3) The pyrolysis product is acid-washed, and then solid-liquid separated, washed and dried.

[0052] According to some embodiments of the present invention, the preparation method of the nitrogen-doped nanocarbon cage is achieved by using a specific nitrogen-containing organic carboxylic acid and controlling the specific ratio of the transition metal salt to the specific nitrogen-containing organic carboxylic acid to prepare the nitrogen-doped nanocarbon cage. The nitrogen-doped nanocarbon cage has a hollow cage-like structure with a diameter of 2-200 nm. Based on the total molar amount of nitrogen, the molar content of pyrrolic nitrogen and / or pyridinic nitrogen on the surface of the nitrogen-doped nanocarbon cage is greater than 80% by X-ray photoelectron spectroscopy. The preparation method has simple equipment and is easy to operate. In some embodiments, the nitrogen-doped nanocarbon cage can be obtained by simple mixing, pyrolysis and acid washing in a pure water phase and under normal pressure conditions.

[0053] According to some embodiments of the present invention, in step (1), the molar ratio of the transition metal salt calculated as the transition metal element to the nitrogen-containing organic carboxylic acid is 1:0.5-1, preferably 1:0.6-0.9. The molar ratio of the transition metal salt calculated as the transition metal element to the nitrogen-containing organic carboxylic acid within the above-defined range is advantageous for controlling the nitrogen content and the type of nitrogen species, so that the nitrogen on the surface of the obtained nitrogen-doped nanocarbon cage exists in the form of pyrrolic nitrogen and / or pyridinic nitrogen.

[0054] According to some embodiments of the present invention, in step (1), there is no particular limitation on the method for forming the solution. For example, the solution may be formed by heating, more preferably by heating and stirring. The present invention also does not particularly limit the heating temperature and stirring rate, as long as the solution can be formed.

[0055] According to some embodiments of the present invention, preferably, in step (1), the precursor is a precursor obtained by dissolving a transition metal salt and a nitrogen-containing organic carboxylic acid in a solvent to form a homogeneous solution, and then removing the solvent in the homogeneous solution. The present invention has no particular limitation on the type of the solvent, and is subject to the ability to form a homogeneous solution. Preferably, the solvent is water and / or ethanol, more preferably water; the present invention has no particular limitation on the amount of the solvent, and is also subject to the ability to form a homogeneous solution. The solvent in the homogeneous solution can be removed by direct evaporation, and the temperature and process of evaporation can adopt existing technologies known to those skilled in the art. For example, the solvent in the homogeneous solution can be removed by heating and evaporating to dryness.

[0056] According to some embodiments of the present invention, preferably, in step (1), the transition metal salt is selected from at least one of an organic acid salt of a transition metal, a carbonate of a transition metal and a basic carbonate of a transition metal, preferably a carbonate of a transition metal and / or a basic carbonate of a transition metal.

[0057] According to some embodiments of the present invention, preferably, the transition metal is a Group VIII metal, preferably at least one of iron, cobalt, nickel and copper, more preferably nickel.

[0058] According to some embodiments of the present invention, preferably, the transition metal salt is selected from basic nickel carbonate and / or nickel acetate.

[0059] According to some embodiments of the present invention, in step (2), the temperature of the high-temperature pyrolysis is 850-1000° C., preferably, the temperature of the high-temperature pyrolysis is 850-950° C. In the present invention, the temperature of the high-temperature pyrolysis can adjust the type of nitrogen species and the removal rate of transition metals. If the temperature is too low, it is not conducive to the removal of transition metals in the material, while if the temperature is too high, nitrogen-doped nanocarbon cages containing other nitrogen species are easily generated.

[0060] According to some embodiments of the present invention, preferably, the high-temperature pyrolysis process includes: heating to the high-temperature pyrolysis temperature at a rate of 0.5-30°C / min, preferably 1-20°C / min, and further preferably 5-10°C / min, and then maintaining a constant temperature; preferably, the constant temperature time is 20-600 min, preferably 60-480 min.

[0061] According to a preferred embodiment of the present invention, in step (2), the temperature is raised to the high-temperature pyrolysis temperature by a two-stage heating method, specifically: first, the temperature is raised to 400-800°C, preferably 500-700°C, at a rate of 1-20°C / min, preferably at a rate of 5-10°C / min, and kept at a constant temperature for 20-600min, preferably 60-480min, and then continued to be raised to the high-temperature pyrolysis temperature at a rate of 1-20°C / min, preferably at a rate of 5-10°C / min, and kept at a constant temperature for 20-600min, preferably 60-480min. In the present invention, the use of a two-stage heating method for heating is conducive to the formation of nitrogen-doped nanocarbon cages containing only pyrrole nitrogen in the nitrogen species or only pyrrole nitrogen and pyridinic nitrogen in the nitrogen species.

[0062] According to some embodiments of the present invention, preferably, in step (2), the inert atmosphere is provided by at least one of nitrogen, argon, neon and helium; and / or

[0063] The reducing atmosphere is provided by hydrogen and, optionally, an inert gas, which is at least one of nitrogen, argon, neon, and helium.

[0064] According to some embodiments of the present invention, in step (3), the pyrolysis product is pickled with a pickling agent, specifically by mixing the pyrolysis product with the pickling agent. The present invention does not particularly limit the mixing method, and the mixing can be carried out by ultrasonic or stirring. The pickling agent can be an acid commonly used in the art, as long as it can remove the transition metals in the pyrolysis product. Preferably, the pickling agent is an aqueous solution of an inorganic acid and / or an aqueous solution of an organic acid, preferably at least one of an aqueous solution of hydrochloric acid, an aqueous solution of sulfuric acid, an aqueous solution of nitric acid, and an aqueous solution of citric acid, more preferably an aqueous solution of hydrochloric acid; preferably, the concentration of the aqueous solution of an inorganic acid and / or an aqueous solution of an organic acid is 0.1-10 mol / L; and the pH value of the pickling agent is less than 7. The present invention has no particular requirements for the amount of the pickling agent, as long as it can remove the transition metals in the pyrolysis product.

[0065] According to some embodiments of the present invention, preferably, in step (3), the pickling temperature is 20-120° C., preferably 60-100° C.; and the pickling time is 0.1-48 h, preferably 4-12 h.

[0066] According to some embodiments of the present invention, in step (3), there is no particular limitation on the solid-liquid separation method, and the solid-liquid separation method known in the art can be used, for example, filtration can be used.

[0067] According to some embodiments of the present invention, the washing is used to remove the acid and metal ions remaining on the nitrogen-doped nanocarbon cages during the acid washing process. Therefore, various water washing methods that can wash the nitrogen-doped nanocarbon cages to neutrality are applicable to the present invention.

[0068] According to some embodiments of the present invention, the drying is used to remove water from the nitrogen-doped nanocarbon cages. Drying can be performed at normal pressure or reduced pressure. Drying conditions may include: a temperature of 80-140° C. and a time of 6-10 hours.

[0069] According to some embodiments of the present invention, preferably, the amounts of the transition metal salt and the nitrogen-containing organic carboxylic acid are such that the molar content of carbon on the surface of the obtained nitrogen-doped nanocarbon cage is 89-92%, the molar content of nitrogen is 1-3%, and the molar content of oxygen is 5-10%.

[0070] According to some embodiments of the present invention, preferably, the amount of the transition metal salt and the nitrogen-containing organic carboxylic acid is such that the nitrogen on the surface of the obtained nitrogen-doped nanocarbon cage is mainly in the form of pyrrolic nitrogen and / or pyridinic nitrogen, and the molar content of pyrrolic nitrogen and / or pyridinic nitrogen in the nitrogen on the surface of the nitrogen-doped nanocarbon cage measured by X-ray photoelectron spectroscopy is greater than 80%, preferably greater than 90%, based on the total molar amount of nitrogen.

[0071] A third aspect of the present invention provides a nitrogen-doped nanocarbon cage prepared by the preparation method described in the second aspect. The nitrogen-doped nanocarbon cage has a hollow cage-like structure, and the diameter of the nitrogen-doped nanocarbon cage is 2-200 nm, preferably 2-100 nm, more preferably 5-50 nm, and even more preferably 5-20 nm. The molar content of pyrrolic nitrogen and / or pyridinic nitrogen in the nitrogen on the surface of the nitrogen-doped nanocarbon cage, as measured by X-ray photoelectron spectroscopy, is greater than 80%, preferably greater than 90%, based on the total molar amount of nitrogen.

[0072] According to some embodiments of the present invention, preferably, the molar ratio of pyrrolic nitrogen to pyridinic nitrogen in the nitrogen on the surface of the nitrogen-doped nanocarbon cage measured by X-ray photoelectron spectroscopy is greater than 2, preferably greater than 3.

[0073] According to some embodiments of the present invention, preferably, the molar content of pyrrolic nitrogen in the nitrogen on the surface of the nitrogen-doped nanocarbon cage measured by X-ray photoelectron spectroscopy is 85.8-100%, and the molar content of pyridinic nitrogen is 0-14.2%, more preferably, the molar content of pyrrolic nitrogen is 100%.

[0074] According to some embodiments of the present invention, the nitrogen-doped nanocarbon cage may contain doping elements that are known to those skilled in the art and can be applied to carbon materials. Preferably, the nitrogen-doped nanocarbon cage does not contain elements such as nickel, sulfur, boron, phosphorus, fluorine, chlorine, bromine, and iodine.

[0075] A fourth aspect of the present invention provides a use of the nitrogen-doped nanocarbon cages described in the first or third aspects in a fuel cell catalyst support and / or fuel cell catalyst. The fuel cell catalyst comprises a support and metal Pt supported on the support, wherein the support is the nitrogen-doped nanocarbon cages described in the first or third aspects.

[0076] According to some embodiments of the present invention, the fuel cell catalyst can be prepared using a method for preparing a fuel cell catalyst known in the art, and the present invention is not particularly limited thereto. Preferably, the method for preparing the fuel cell catalyst comprises:

[0077] (a) dispersing nitrogen-doped carbon nanocages in a solvent, and then adding a platinum compound to the solvent in which the nitrogen-doped carbon nanocages are dispersed to obtain a suspension;

[0078] (b) contacting a reducing agent with the suspension.

[0079] According to some embodiments of the present invention, the solvent can be any solvent known in the art for preparing fuel cell catalysts, preferably at least one of water, ethanol, and ethylene glycol. Preferably, the amount of the solvent used is 50-1500 mL per gram of nitrogen-doped nanocarbon cages.

[0080] According to some embodiments of the present invention, the platinum compound can be any platinum compound known in the art for use in preparing fuel cell catalysts, such as at least one of chloroplatinic acid, chloroplatinates, platinum chloride, platinum nitrate, and platinum complexes, preferably chloroplatinic acid. Preferably, the molar ratio of the nitrogen-doped nanocarbon cage to the platinum compound, calculated as elemental platinum, is 10-70:1.

[0081] According to some embodiments of the present invention, the reducing agent can be a reducing agent known in the art, for example, at least one of formaldehyde, formic acid, sodium thiosulfate, sodium borohydride and potassium borohydride, preferably formic acid. Preferably, the molar ratio of the reducing agent to the platinum compound calculated as platinum element is 2-10:1

[0082] According to some embodiments of the present invention, preferably, the pH of the suspension is 9-11.

[0083] According to some embodiments of the present invention, preferably, the reducing agent is contacted with the suspension at a temperature of 30-90° C. for a contact time of 0.1-8 hours. Preferably, after contacting the reducing agent with the suspension, the method further comprises filtering the reaction mixture, washing the filter cake obtained by filtration, and drying the filter cake.

[0084] According to some embodiments of the present invention, preferably, based on the total weight of the fuel cell catalyst, the loading amount of Pt in the fuel cell catalyst is 20-70 wt %.

[0085] The nitrogen on the surface of the nitrogen-doped nanocarbon cage provided by the present invention exists in the form of pyrrole nitrogen and / or pyridinic nitrogen. Based on the total molar amount of nitrogen, the molar content of pyrrole nitrogen and / or pyridinic nitrogen in the nitrogen on the surface of the nitrogen-doped nanocarbon cage measured by X-ray photoelectron spectroscopy is greater than 80%, which is beneficial to improving the oxygen reduction reaction (ORR) activity of the fuel cell catalyst (Pt / C catalyst) and can be used as a carrier in the fuel cell catalyst. Since the present invention only involves the improvement of the carrier, when the nitrogen-doped nanocarbon cage of the present invention is applied to the fuel cell catalyst, there is no special restriction on the other composition and structure of the fuel cell catalyst. When the Pt / C catalyst prepared by the nitrogen-doped nanocarbon cage provided by the present invention is applied to the redox reaction, the half-wave potential is 0.869-0.890V and the limiting current density is 5.969-6.51mA cm -2 , the kinetic current density is 3.075-4.791 mA cm -2 , electrochemically active area (ECSA) is 51.8-58.5m 2 g -1 -Pt, mass specific activity of 0.151-0.235A mg -1 -Pt, with an area specific activity of 0.291-0.425 mA mg -1 -Pt, which has higher electrochemical activity.

[0086] The present invention will be described in detail below through examples.

[0087] Unless otherwise specified, all reagents used in the present invention are of analytical grade and commercially available.

[0088] The surface morphology of the material was characterized using high-resolution transmission electron microscopy (HRTEM). The microscope used was a JEM-2100 (JEOL Ltd.) at an accelerating voltage of 200 kV. The diameter of the nitrogen-doped nanocarbon cages was measured using HRTEM images.

[0089] The pore structure properties of the material were determined using the BET test method. Specifically, a Quantachrome AS-6B analyzer was used for measurement. The specific surface area and pore volume of the material were obtained using the Brunauer-Emmett-Taller (BET) method, and the mesopore distribution curve was calculated from the desorption curve using the Barrett-Joyner-Halenda (BJH) method.

[0090] The content of each element on the surface of the material was determined by X-ray photoelectron spectroscopy (XPS). The X-ray photoelectron spectroscopy analysis was performed on an ESCALab250 X-ray photoelectron spectrometer equipped with Thermo Avantage V5.926 software from Thermo Scientific. The excitation source was monochromatic Al Kα X-ray with an energy of 1486.6 eV and a power of 150 W. The penetration energy used for narrow scanning was 30 eV. The base vacuum during the analysis was 6.53×10 -9 The electron binding energy was calibrated using the C1s peak of elemental carbon (284.6 eV). Data were processed using Thermo Avantage software, and the sensitivity factor method was used for quantitative analysis in the analysis module.

[0091] The graphitization degree of the material was characterized by Raman spectroscopy, 1355 cm -1 The peak at 1585 cm (D peak) is attributed to structural defects and is amorphous carbon. -1 The peak (G peak) is attributed to the carbon in the planar structure. Usually I D / I G (D peak and G peak intensity ratio) to characterize the degree of graphitization of the material. D / I G The higher the value, the more defects there are and the lower the degree of graphitization. The Raman spectrum of the material was obtained using a RM2000 micro-confocal Raman spectrometer (product of Reinshaw Company). Technical specifications: The excitation source used was a He-Ne laser with a wavelength of 525 nm.

[0092] The electrochemical performance of the Pt / C catalyst was tested in accordance with GB / T 20042.4-2009 Test method for proton exchange membrane fuel cell electrocatalysts.

[0093] Examples 1-4 are used to illustrate nitrogen-doped nanocarbon cages and their preparation methods.

[0094] Example 1

[0095] (1) Weigh 15 g of basic nickel carbonate and 20.9 g of ethylenediaminetetraacetic acid (molar ratio of 1:0.7) and add them to a beaker containing 40 mL of deionized water. Stir and mix them at 80 °C until uniform, and continue heating and evaporating to obtain a solid precursor.

[0096] (2) The precursor obtained in step (1) was placed in a porcelain boat, and then the porcelain boat was placed in the constant temperature zone of a tube furnace, nitrogen was introduced at a flow rate of 80 mL / min, and the temperature was raised to 600°C at a rate of 10°C / min. After the constant temperature was maintained for 1 hour, the temperature was continued to be raised to 900°C at a rate of 10°C / min, and the temperature was maintained for 2 hours. The heating was stopped, and the mixture was cooled to room temperature under a nitrogen atmosphere to obtain a pyrolysis product.

[0097] (3) The pyrolysis product obtained in step (2) was added to an aqueous solution containing 2M hydrochloric acid and stirred at 90°C for 8 hours, then filtered, the filtrate was collected, and then washed with deionized water until the filtrate was neutral. The filter cake was then dried in a constant temperature oven at 120°C for 6 hours to obtain nitrogen-doped nanocarbon cages.

[0098] Figure 1 TEM image of the nitrogen-doped nanocarbon cage. It can be seen from the image that the nitrogen-doped nanocarbon cage is a hollow cage-shaped nanocarbon material with a diameter of 5-20 nm.

[0099] Figure 2 This is the XPS spectrum of the nitrogen-doped nanocarbon cage. It can be seen from the figure that in addition to carbon, oxygen and nitrogen elements are also present on the surface of the nitrogen-doped nanocarbon cage. The atomic molar percentage of each element can be calculated from the peak area, among which carbon is 90.06%, oxygen is 8.4%, and nitrogen is 1.54%.

[0100] Figure 3 This is the N1s peak spectrum of the XPS of the nitrogen-doped nanocarbon cage. It can be seen from the figure that the nitrogen on the surface of the nitrogen-doped nanocarbon cage exists in the form of pyrrole nitrogen, and there is no other form of nitrogen species. Based on the total molar amount of nitrogen, the content of pyrrole nitrogen is 100%.

[0101] BET test shows that the BET specific surface area of ​​the nitrogen-doped nanocarbon cage is 466.24 m 2 / g, pore volume 0.978cm 3 / g. Figure 4 is the BJH pore size distribution curve of the nitrogen-doped nanocarbon cage. As can be seen from the figure, the pore size distribution curve of the nitrogen-doped nanocarbon cage has two mesopore distribution peaks at 3.68 nm and 6.15 nm.

[0102] Raman analysis showed that the nitrogen-doped nanocarbon cage had obvious D peak and G peak. D / I G It is 0.5266, indicating that the nitrogen-doped nanocarbon cage has a certain degree of graphitization.

[0103] Example 2

[0104] (1) Weigh 15 g of basic nickel carbonate and 20.9 g of ethylenediaminetetraacetic acid (molar ratio of 1:0.7) and add them to a beaker containing 40 mL of deionized water. Stir and mix them at 80 °C until uniform, and continue heating and evaporating to obtain a solid precursor.

[0105] (2) The precursor obtained in step (1) was placed in a porcelain boat, and then the porcelain boat was placed in the constant temperature zone of a tube furnace, nitrogen was introduced at a flow rate of 80 mL / min, and the temperature was raised to 600°C at a rate of 10°C / min. After the temperature was kept constant for 1 hour, the temperature was continued to be raised to 850°C at a rate of 10°C / min, and the temperature was kept constant for 2 hours. The heating was stopped, and the mixture was cooled to room temperature under a nitrogen atmosphere to obtain a pyrolysis product.

[0106] (3) The pyrolysis product obtained in step (2) was added to an aqueous solution containing 2M hydrochloric acid and stirred at 100°C for 8 hours, then filtered, the filtrate was collected, and then washed with deionized water until the filtrate was neutral. The filter cake was then dried in a constant temperature oven at 120°C for 6 hours to obtain nitrogen-doped nanocarbon cages.

[0107] High-resolution transmission electron microscopy observation and measurement show that the nitrogen-doped nanocarbon cage has a hollow cage-like structure with a diameter of 5-20 nm.

[0108] XPS measurements show that in addition to carbon, oxygen and nitrogen are present on the surface of the nitrogen-doped nanocarbon cage. The atomic percentage of each element can be calculated from the peak area, where carbon is 91.05%, oxygen is 7.48%, and nitrogen is 1.47%. The nitrogen element of the nitrogen-doped nanocarbon cage is separated into peaks, as shown in Figure 2. Figure 5 As shown in the figure, it can be seen that the nitrogen on the surface of the nitrogen-doped nanocarbon cage exists in two forms: pyrrolic nitrogen and pyridinic nitrogen. Based on the total molar amount of nitrogen, the content of pyrrolic nitrogen is 92.01% and the content of pyridinic nitrogen is 7.99%.

[0109] BET test shows that the BET specific surface area of ​​the nitrogen-doped nanocarbon cage is 713.17 m 2 / g, pore volume 1.482cm 3 In the BJH pore size distribution curve of the nitrogen-doped nanocarbon cage, there are two mesopore distribution peaks at 3.71 nm and 6.25 nm.

[0110] Raman analysis showed that the nitrogen-doped nanocarbon cage had obvious D peak and G peak. D / I G It is 0.703, indicating that the nitrogen-doped nanocarbon cage has a certain degree of graphitization.

[0111] Example 3

[0112] (1) Weigh 15 g of nickel acetate and 22.3 g of ethylenediaminetetraacetic acid (molar ratio of 1:0.9), add them to a beaker containing 40 mL of deionized water, stir and mix at 80 °C, and continue heating and evaporating to obtain a solid precursor.

[0113] (2) The precursor obtained in step (1) is placed in a porcelain boat, which is then placed in the constant temperature zone of a tube furnace. Nitrogen gas is introduced at a flow rate of 150 mL / min, and the temperature is raised to 950°C at a rate of 20°C / min. After maintaining the constant temperature for 2 hours, heating is stopped, and the mixture is cooled to room temperature under a nitrogen atmosphere to obtain a pyrolysis product.

[0114] (3) The pyrolysis product obtained in step (2) was added to an aqueous solution containing 2M nitric acid and stirred at 100°C for 8 hours, then filtered, the filtrate was collected, and then washed with deionized water until the filtrate was neutral. The filter cake was then dried in a constant temperature oven at 120°C for 6 hours to obtain nitrogen-doped nanocarbon cages.

[0115] High-resolution transmission electron microscopy observation and measurement show that the nitrogen-doped nanocarbon cage has a hollow cage-like structure with a diameter of 5-20 nm.

[0116] XPS measurements show that in addition to carbon, oxygen and nitrogen are present on the surface of the nitrogen-doped nanocarbon cage. The atomic percentage of each element can be calculated from the peak area, where carbon is 89.96%, oxygen is 7.97%, and nitrogen is 2.07%. The nitrogen element of the nitrogen-doped nanocarbon cage is separated into peaks, as shown in Figure 2. Figure 6 As shown in the figure, it can be seen that the nitrogen on the surface of the nitrogen-doped nanocarbon cage exists in two forms: pyrrolic nitrogen and pyridinic nitrogen. Based on the total molar amount of nitrogen, the content of pyrrolic nitrogen is 85.80% and the content of pyridinic nitrogen is 14.20%.

[0117] BET test shows that the BET specific surface area of ​​the nitrogen-doped nanocarbon cage is 512.17 m 2 / g, pore volume 1.123cm 3 In the BJH pore size distribution curve of the nitrogen-doped nanocarbon cage, there are two mesopore distribution peaks at 3.59 nm and 9.25 nm.

[0118] Raman analysis showed that the nitrogen-doped nanocarbon cage had obvious D peak and G peak. D / I G It is 0.324, indicating that the nitrogen-doped nanocarbon cage has a certain degree of graphitization.

[0119] Example 4

[0120] (1) Weigh 15 g of nickel acetate and 14.87 g of ethylenediaminetetraacetic acid (molar ratio of 1:0.6) and add them to a beaker containing 40 mL of deionized water. Stir and mix them at 80 °C until uniform, and continue heating and evaporating to obtain a solid precursor.

[0121] (2) The precursor obtained in step (1) was placed in a porcelain boat, which was then placed in the constant temperature zone of a tube furnace. Nitrogen was introduced at a flow rate of 50 mL / min, and the temperature was raised to 900°C at a rate of 10°C / min. After maintaining the constant temperature for 3 hours, heating was stopped, and the mixture was cooled to room temperature under a nitrogen atmosphere to obtain a pyrolysis product.

[0122] (3) The pyrolysis product obtained in step (2) was added to an aqueous solution containing 2M nitric acid and stirred at 90°C for 8 hours, then filtered, the filtrate was collected, and then washed with deionized water until the filtrate was neutral. The filter cake was then dried in a constant temperature oven at 120°C for 6 hours to obtain nitrogen-doped nanocarbon cages.

[0123] High-resolution transmission electron microscopy observation and measurement show that the nitrogen-doped nanocarbon cage has a hollow cage-like structure with a diameter of 5-20 nm.

[0124] XPS measurements show that in addition to carbon, oxygen and nitrogen are present on the surface of the nitrogen-doped nanocarbon cage. The atomic percentage of each element can be calculated from the peak area, where carbon is 93.14%, oxygen is 5.44%, and nitrogen is 1.42%. The nitrogen element of the nitrogen-doped nanocarbon cage is separated into peaks, as shown in Figure 2. Figure 7 As shown in the figure, it can be seen that the nitrogen on the surface of the nitrogen-doped nanocarbon cage exists in the form of pyrrole nitrogen, and no other forms of nitrogen species exist. Based on the total molar amount of nitrogen, the content of pyrrole nitrogen is 100%.

[0125] BET test shows that the BET specific surface area of ​​the nitrogen-doped nanocarbon cage is 435.207 m 2 / g, pore volume 0.734cm 3 In the BJH pore size distribution curve of the nitrogen-doped nanocarbon cage, there are two mesopore distribution peaks at 3.79 nm and 6.231 nm.

[0126] Raman analysis showed that the nitrogen-doped nanocarbon cage had obvious D peak and G peak. D / I G It is 0.4689, indicating that the nitrogen-doped nanocarbon cage has a certain degree of graphitization.

[0127] Comparative Example 1

[0128] (1) Weigh 15 g of basic nickel carbonate and 20.9 g of ethylenediaminetetraacetic acid (molar ratio of 1:0.7) and add them to a beaker containing 40 mL of deionized water. Stir and mix them at 80 °C until uniform, and continue heating and evaporating to obtain a solid precursor.

[0129] (2) The precursor obtained in step (1) was placed in a porcelain boat, and then the porcelain boat was placed in the constant temperature zone of a tube furnace, nitrogen was introduced at a flow rate of 80 mL / min, and the temperature was increased to 600°C at a rate of 10°C / min. After the constant temperature was maintained for 1 hour, the temperature was continued to be increased to 1100°C at a rate of 10°C / min, and the temperature was maintained for 2 hours. The heating was stopped, and the mixture was cooled to room temperature under a nitrogen atmosphere to obtain a pyrolysis product.

[0130] (3) The pyrolysis product obtained in step (2) was added to an aqueous solution containing 1M sulfuric acid and stirred at 80°C for 8 hours, then filtered, the filtrate was collected, and then washed with deionized water until the filtrate was neutral. The filter cake was then dried in a constant temperature oven at 120°C for 8 hours to obtain nitrogen-doped nanocarbon cages.

[0131] High-resolution transmission electron microscopy observation and measurement show that the nitrogen-doped nanocarbon cage has a hollow cage-like structure with a diameter of 5-20 nm.

[0132] XPS measurements show that in addition to carbon, oxygen and nitrogen are present on the surface of the nitrogen-doped nanocarbon cage. The atomic percentage of each element can be calculated from the peak area, where carbon is 89.9%, oxygen is 8.52%, and nitrogen is 1.58%. The nitrogen element of the nanocarbon cage is separated into peaks, as shown in Figure 2. Figure 8 As shown in the figure, it can be seen that among the nitrogen species on the surface of the nanocarbon cage, in addition to pyrrolic nitrogen species, there are also graphitic nitrogen species. Based on the total molar amount of nitrogen, the content of pyrrolic nitrogen is 65.16% and the content of graphitic nitrogen is 34.84%.

[0133] BET test shows that the BET specific surface area of ​​the nitrogen-doped nanocarbon cage is 423.27 m 2 / g, pore volume 0.931cm 3 In the BJH pore size distribution curve of the nitrogen-doped nanocarbon cage, there are two mesopore distribution peaks at 3.995 nm and 7.12 nm.

[0134] Comparative Example 2

[0135] (1) Weigh 15 g of basic nickel carbonate and 11.95 g of ethylenediaminetetraacetic acid (molar ratio of 1:0.4) and add them to a beaker containing 40 mL of deionized water. Stir and mix them at 80 °C until uniform, and continue heating and evaporating to obtain a solid precursor.

[0136] (2) The precursor obtained in step (1) was placed in a porcelain boat, and then the porcelain boat was placed in the constant temperature zone of a tube furnace, nitrogen was introduced at a flow rate of 80 mL / min, and the temperature was raised to 600°C at a rate of 10°C / min. After the temperature was kept constant for 1 hour, the temperature was continued to be raised to 800°C at a rate of 10°C / min, and the temperature was kept constant for 2 hours. The heating was stopped, and the mixture was cooled to room temperature under a nitrogen atmosphere to obtain a pyrolysis product.

[0137] (3) The pyrolysis product obtained in step (2) was added to an aqueous solution containing 2M hydrochloric acid and stirred at 100°C for 8 hours, then filtered, the filtrate was collected, and then washed with deionized water until the filtrate was neutral. The filter cake was then dried in a constant temperature oven at 120°C for 6 hours to obtain nitrogen-doped nanocarbon cages.

[0138] High-resolution transmission electron microscopy observation and measurement show that the nitrogen-doped nanocarbon cage has a hollow cage-like structure with a diameter of 5-20 nm.

[0139] XPS measurements show that in addition to carbon, oxygen and nitrogen are present on the surface of the nitrogen-doped nanocarbon cage. The atomic percentage of each element can be calculated from the peak area, where carbon is 96.16%, oxygen is 2.52%, and nitrogen is 1.32%. The nitrogen element of the nitrogen-doped nanocarbon cage is separated into peaks, as shown in Figure 2. Figure 9 As shown in the figure, it can be seen that among the nitrogen species on the surface of the nitrogen-doped nanocarbon cage, in addition to pyrrolic nitrogen species and pyridinic nitrogen species, there are also graphitic nitrogen species and oxidized nitrogen species. Based on the total molar amount of nitrogen, the content of pyrrolic nitrogen is 18.74%, the content of pyridinic nitrogen is 11.75%, the content of graphitic nitrogen is 56.31%, and the content of oxidized nitrogen is 13.19%.

[0140] BET test shows that the BET specific surface area of ​​the nitrogen-doped nanocarbon cage is 579.11 m 2 / g, pore volume 1.257cm 3 In the BJH pore size distribution curve of the nitrogen-doped nanocarbon cage, there are two mesopore distribution peaks at 3.71 nm and 6.25 nm.

[0141] Comparative Example 3

[0142] (1) Weigh 20 g of basic nickel carbonate, 20 g of citric acid, and 4.09 g of urea, add them to a beaker containing 70 mL of deionized water, stir and mix at 80 °C, and continue heating and evaporating to obtain a solid precursor.

[0143] (2) The precursor obtained in step (1) was placed in a porcelain boat, and then the porcelain boat was placed in the constant temperature zone of a tube furnace, nitrogen was introduced at a flow rate of 80 mL / min, and the temperature was raised to 600°C at a rate of 10°C / min. After the constant temperature was maintained for 1 hour, the temperature was continued to be raised to 900°C at a rate of 10°C / min, and the temperature was maintained for 2 hours. The heating was stopped, and the mixture was cooled to room temperature under a nitrogen atmosphere to obtain a pyrolysis product.

[0144] (3) The pyrolysis product obtained in step (2) was added to an aqueous solution containing 2M hydrochloric acid and stirred at 100°C for 8 hours, then filtered, the filtrate was collected, and then washed with deionized water until the filtrate was neutral. The filter cake was then dried in a constant temperature oven at 120°C for 6 hours to obtain nitrogen-doped nanocarbon cages.

[0145] High-resolution transmission electron microscopy observation and measurement show that the nitrogen-doped nanocarbon cage has a hollow cage-like structure with a diameter of 5-20 nm.

[0146] XPS measurements show that in addition to carbon, oxygen and nitrogen are present on the surface of the nitrogen-doped nanocarbon cage. The atomic percentage of each element can be calculated from the peak area, where carbon is 95.64%, oxygen is 4.72%, and nitrogen is 1.44%. The nitrogen element of the nitrogen-doped nanocarbon cage is separated into peaks, as shown in Figure 2. Figure 10 As shown in the figure, it can be seen that among the nitrogen species on the surface of the nitrogen-doped nanocarbon cage, in addition to pyrrolic nitrogen species and pyridinic nitrogen species, there are also graphitic nitrogen species and oxidized nitrogen species. Based on the total molar amount of nitrogen, the content of pyrrolic nitrogen is 24.26%, the content of pyridinic nitrogen is 22.04%, the content of graphitic nitrogen is 30.5%, and the content of oxidized nitrogen is 23.2%.

[0147] BET test shows that the BET specific surface area of ​​the nitrogen-doped nanocarbon cage is 912.473 m 2 / g, pore volume 2.594cm 3 In the BJH pore size distribution curve of the nitrogen-doped nanocarbon cage, there are two mesopore distribution peaks at 3.889 nm and 9.24 nm.

[0148] Comparative Example 4

[0149] (1) Weigh 15 g of basic nickel carbonate and 32.86 g of ethylenediaminetetraacetic acid (molar ratio of 1:1.1), add them to a beaker containing 40 mL of deionized water, stir and mix at 80 °C, and continue heating and evaporating to obtain a solid precursor.

[0150] (2) The precursor obtained in step (1) was placed in a porcelain boat, and then the porcelain boat was placed in the constant temperature zone of a tube furnace, nitrogen was introduced at a flow rate of 80 mL / min, and the temperature was raised to 600°C at a rate of 10°C / min. After the temperature was kept constant for 1 hour, the temperature was continued to be raised to 850°C at a rate of 10°C / min, and the temperature was kept constant for 2 hours. The heating was stopped, and the mixture was cooled to room temperature under a nitrogen atmosphere to obtain a pyrolysis product.

[0151] (3) The pyrolysis product obtained in step (2) was added to an aqueous solution containing 2M hydrochloric acid and stirred at 100°C for 8 hours, then filtered, the filtrate was collected, and then washed with deionized water until the filtrate was neutral. The filter cake was then dried in a constant temperature oven at 120°C for 6 hours to obtain nitrogen-doped nanocarbon cages.

[0152] High-resolution transmission electron microscopy observation and measurement show that the nitrogen-doped nanocarbon cage has a hollow cage-like structure with a diameter of 5-20 nm.

[0153] XPS measurements show that in addition to carbon, oxygen and nitrogen are present on the surface of the nitrogen-doped nanocarbon cage. The atomic percentage of each element can be calculated from the peak area, where carbon is 94.7%, oxygen is 3.29%, and nitrogen is 1.95%. The nitrogen element of the nitrogen-doped nanocarbon cage is separated into peaks, as shown in Figure 2. Figure 11 As shown in the figure, it can be seen that among the nitrogen species on the surface of the material, in addition to pyrrolic nitrogen species and pyridinic nitrogen species, there are also graphitic nitrogen species and oxidized nitrogen species. Based on the total molar amount of nitrogen, the content of pyrrolic nitrogen is 10.20%, the content of pyridinic nitrogen is 21.09%, the content of graphitic nitrogen is 43.01%, and the content of oxidized nitrogen is 25.7%.

[0154] The BET test shows that the BET specific surface area of ​​the material is 320.915 m 2 / g, pore volume 0.809cm 3 In the BJH pore size distribution curve of the material, there are two mesopore distribution peaks at 3.9 nm and 9.12 nm.

[0155] Test Case

[0156] This test example is used to illustrate a fuel cell catalyst and its preparation method.

[0157] Preparation of Pt / C catalyst: 0.6 g of the nitrogen-doped nanocarbon cages obtained in Examples 1-4 was dispersed in 200 mL of deionized water, a certain amount of chloroplatinic acid was added, and ultrasonic dispersion was performed to form a suspension. Then, an aqueous sodium carbonate solution was added to adjust the pH of the suspension to 10; the above suspension was heated to 80°C, and formic acid was added under stirring to carry out a reduction reaction, wherein the molar ratio of the reducing agent to chloroplatinic acid calculated as platinum element was 5:1, and the reaction was maintained for 8 hours; the reaction mixture was filtered, washed until the solution pH was neutral, and dried at 100°C to obtain Pt / C catalysts A1-A4 with a Pt loading of 40% by weight.

[0158] Catalytic performance test of Pt / C catalyst: The prepared Pt / C catalysts A1-A4 were applied to oxygen reduction reaction (ORR) for catalytic performance test, and the corresponding catalytic performance is shown in Table 1.

[0159] Test comparison

[0160] Preparation of Pt / C catalyst: 0.6 g of the nitrogen-doped nanocarbon cages obtained in Comparative Examples 1-4 were respectively dispersed in 200 mL of deionized water, a certain amount of chloroplatinic acid was added, and ultrasonic dispersion was performed to form a suspension, and then a sodium carbonate aqueous solution was added to adjust the pH of the suspension to 10; the above suspension was heated to 80°C, and formic acid was added under stirring to carry out a reduction reaction, wherein the molar ratio of the reducing agent to chloroplatinic acid calculated as platinum element was 5:1, and the reaction was maintained for 8 hours; the mixture after the reaction was filtered, washed until the pH of the solution was neutral, and dried at 100°C to obtain Pt / C catalysts D1-D4 with a Pt loading of 40 weight%.

[0161] According to the method of the test example, the prepared Pt / C catalysts D1-D4 were applied to the oxygen reduction reaction (ORR) for catalytic performance testing, and the corresponding catalytic performance is shown in Table 1.

[0162] Table 1

[0163]

[0164] From the above data, it can be seen that when the nitrogen-doped nanocarbon cage provided by the present invention is used as a carrier for a fuel cell catalyst (Pt / C catalyst), the half-wave potential is 0.869-0.890 V and the limiting current density is 5.969-6.51 mA cm -2 , the kinetic current density is 3.075-4.791 mA cm -2 , electrochemically active area (ECSA) is 51.8-58.5m 2 g -1 -Pt, mass specific activity of 0.151-0.235A mg -1 -Pt, with an area specific activity of 0.291-0.425 mA mg -1 -Pt, that is, the Pt / C catalyst prepared by the nitrogen-doped nanocarbon cage provided by the present invention has higher electrochemical activity.

[0165] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A nitrogen-doped nanocarbon cage, characterized in that The nitrogen-doped nanocarbon cage has a hollow cage-like structure, and the diameter of the nitrogen-doped nanocarbon cage is 2-200 nm. Based on the total molar amount of nitrogen, the molar content of pyrrolic nitrogen in the nitrogen on the surface of the nitrogen-doped nanocarbon cage is 92.01-100%, and the molar content of pyridinic nitrogen is 0-7.99% as measured by X-ray photoelectron spectroscopy; The nitrogen on the surface of the nitrogen-doped nanocarbon cage exists in the form of pyrrolic nitrogen and pyridinic nitrogen; The nitrogen-doped nanocarbon cage has a double mesopore distribution peak, and the double mesopore distribution peaks correspond to a first most probable pore diameter and a second most probable pore diameter, respectively. The first most probable pore diameter is 3.5-4 nanometers, and the second most probable pore diameter is 6-9.5 nanometers.

2. The nitrogen-doped nanocarbon cage according to claim 1, wherein The diameter of the nitrogen-doped nanocarbon cage is 2-100 nm; And / or, the molar ratio of pyrrolic nitrogen to pyridinic nitrogen in the nitrogen on the surface of the nitrogen-doped nanocarbon cage is greater than 2 as measured by X-ray photoelectron spectroscopy.

3. The nitrogen-doped nanocarbon cage according to claim 2, wherein The diameter of the nitrogen-doped nanocarbon cage is 5-50 nm; And / or, the molar ratio of pyrrolic nitrogen to pyridinic nitrogen in the nitrogen on the surface of the nitrogen-doped nanocarbon cage is greater than 3 as measured by X-ray photoelectron spectroscopy.

4. The nitrogen-doped nanocarbon cage according to claim 3, wherein The diameter of the nitrogen-doped nanocarbon cage is 5-20 nm.

5. The nitrogen-doped nanocarbon cage according to claim 1 or 2, wherein X-ray photoelectron spectroscopy measured the molar content of carbon on the surface of the nitrogen-doped nanocarbon cage to be 89-92%, the molar content of nitrogen to be 1-3%, and the molar content of oxygen to be 5-10%.

6. The nitrogen-doped nanocarbon cage according to claim 1 or 2, wherein: The BET specific surface area of ​​the nitrogen-doped nanocarbon cage is greater than 300 m 2 / g, with a total pore volume greater than 0.6 cm 3 / g.

7. The nitrogen-doped nanocarbon cage according to claim 6, wherein The BET specific surface area of ​​the nitrogen-doped nanocarbon cage is greater than 460 m 2 / g, with a total pore volume greater than 0.7 cm 3 / g.

8. The nitrogen-doped nanocarbon cage according to claim 1 or 2, wherein In the Raman curve of the nitrogen-doped nanocarbon cage, I D / I G The range is 0.2-1.

9. The nitrogen-doped nanocarbon cage according to claim 8, wherein In the Raman curve of the nitrogen-doped nanocarbon cage, I D / I G The range is 0.3-0.

8.

10. A method for preparing the nitrogen-doped nanocarbon cage according to any one of claims 1 to 9, characterized in that: The method comprises the following steps: (1) providing a solution containing a transition metal salt, a nitrogen-containing organic carboxylic acid, and a solvent, and then drying to obtain a precursor, wherein the nitrogen-containing organic carboxylic acid is ethylenediaminetetraacetic acid; and the molar ratio of the transition metal salt to the nitrogen-containing organic carboxylic acid, calculated as the transition metal element, is 1:0.5-1; (2) Under an inert atmosphere or a reducing atmosphere, the precursor obtained in step (1) is subjected to high-temperature pyrolysis, wherein the temperature of the high-temperature pyrolysis is 850-1000°C to obtain a pyrolysis product; the high-temperature pyrolysis process comprises: first heating the temperature to 400-800°C at a rate of 1-20°C / min, maintaining the temperature for 20-600 minutes, and then continuing to heat the temperature at a rate of 1-20°C / min to the high-temperature pyrolysis temperature, and maintaining the temperature for 20-600 minutes; (3) The pyrolysis product is acid-washed, and then solid-liquid separation, washing and drying are performed.

11. The preparation method according to claim 10, wherein In step (1), the molar ratio of the transition metal salt to the nitrogen-containing organic carboxylic acid is 1:0.6-0.9, calculated as the transition metal element.

12. The preparation method according to claim 10, wherein In step (1), the transition metal salt is selected from at least one of an organic acid salt of a transition metal, a carbonate of a transition metal, and a basic carbonate of a transition metal; And / or, the transition metal is a Group VIII metal.

13. The preparation method according to claim 12, wherein In step (1), the transition metal salt is a transition metal carbonate and / or a transition metal basic carbonate; And / or, the transition metal is at least one of iron, cobalt, nickel and copper.

14. The preparation method according to claim 13, wherein The transition metal is nickel.

15. The preparation method according to claim 10, wherein In step (1), the solvent is water.

16. The preparation method according to claim 10, wherein In step (2), the temperature of the high-temperature pyrolysis is 850-950°C.

17. The preparation method according to claim 16, wherein The high-temperature pyrolysis process comprises: heating to the high-temperature pyrolysis temperature at a rate of 1-20°C / min, and then maintaining a constant temperature; and / or, the constant temperature time is 60-480 minutes; And / or, the high-temperature pyrolysis process includes: first heating to 500-700°C at a rate of 5-10°C / min, maintaining the temperature for 60-480 minutes, then continuing to heat to the high-temperature pyrolysis temperature at a rate of 5-10°C / min, and maintaining the temperature for 60-480 minutes.

18. The preparation method according to claim 17, wherein The high-temperature pyrolysis process includes: heating to the high-temperature pyrolysis temperature at a rate of 5-10°C / min, and then maintaining a constant temperature.

19. The preparation method according to claim 10, wherein In step (2), the inert atmosphere is provided by at least one of nitrogen, argon, neon and helium; and / or The reducing atmosphere is provided by hydrogen and optionally an inert gas.

20. The preparation method according to claim 10, wherein In step (3), the pickling agent used for pickling the pyrolysis product is an inorganic acid aqueous solution and / or an organic acid aqueous solution; and / or, the pH value of the inorganic acid aqueous solution or the organic acid aqueous solution is less than 7; And / or, in step (3), the pickling temperature is 20-120°C and the time is 0.1-48h.

21. The preparation method according to claim 20, wherein In step (3), the pickling agent used for pickling the pyrolysis product is at least one of a hydrochloric acid aqueous solution, a sulfuric acid aqueous solution, a nitric acid aqueous solution and a citric acid aqueous solution; The pickling temperature is 60-100° C. and the pickling time is 4-12 hours.

22. The preparation method according to claim 21, wherein In step (3), the pickling agent used for pickling the pyrolysis product is a hydrochloric acid aqueous solution.

23. Use of the nitrogen-doped nanocarbon cage according to any one of claims 1 to 9 in a fuel cell catalyst support and / or fuel cell catalyst.

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