An ultrahigh pressure assisted prepared sheet-like Fe-N-C electrocatalyst and a preparation method thereof

Abstract

This invention discloses a layered Fe-N-C electrocatalyst prepared under ultra-high pressure assisted conditions and its preparation method, belonging to the field of electrocatalyst technology. Using Fe-TPTZ metal complex as a precursor and fumed silica as a hard template, the two are uniformly mixed and then subjected to a six-sided press at 3-6 GPa ultra-high pressure conditions, heated to 1000℃ and held under pressure. After post-treatment to remove the template, the target catalyst is obtained. This invention utilizes the above-mentioned layered Fe-N-C electrocatalyst prepared under ultra-high pressure assisted conditions and its preparation method. By controlling the ultra-high pressure field, the precise construction of the catalyst layer morphology and the highly active metastable Fe-N... x The controllable synthesis of coordination phases significantly improves the electrocatalytic activity, preparation efficiency, and cycle stability of the catalyst.

Description

Technical Field

[0001] This invention relates to the field of electrocatalyst technology, and in particular to a layered Fe-NC electrocatalyst prepared under ultra-high pressure and its preparation method. Background Technology

[0002] With the rapid development of the new energy industry, electrochemical energy devices such as fuel cells have become a research hotspot due to their high energy density and clean, environmentally friendly advantages. The oxygen reduction reaction, as its core electrode reaction, is a slow-moving kinetic process, urgently requiring efficient catalysts to lower the reaction energy barrier. Currently, commercial platinum-based catalysts suffer from scarcity and high cost, severely restricting the large-scale deployment of related devices. Fe-NC-based non-precious metal catalysts, on the other hand, are widely recognized as the most promising alternative to platinum-based catalysts due to their wide availability of raw materials, low cost, and excellent catalytic activity.

[0003] Currently, the mainstream preparation process for Fe-NC catalysts is atmospheric pressure pyrolysis, which involves mixing precursors such as iron sources, nitrogen-containing organic ligands, and carbon sources, and then carbonizing them at high temperatures of 800-1000℃ under an inert atmosphere at atmospheric pressure. However, this process has many insurmountable technical bottlenecks. During pyrolysis, the decomposition and volatilization of organic matter can easily cause pore structure collapse. The morphology control methods are limited, making it difficult to construct ordered lamellar structures. At the same time, a large number of active sites are buried or insufficiently exposed, which increases the mass transfer resistance of the electrochemical reaction. Due to the limitations of atmospheric pressure thermodynamic conditions, it is impossible to stably synthesize metastable metal-nitrogen coordination structures that are difficult to exist under atmospheric pressure, making it difficult to break through the upper limit of catalytic performance. The gas-solid phase reaction rate at atmospheric pressure is slow, and pyrolysis holding usually requires several hours, resulting in a long preparation cycle, high production energy consumption, and susceptibility to airflow disturbances during large-scale production, making it difficult to guarantee batch-to-batch uniformity of products. The carbon matrix prepared at atmospheric pressure is not dense enough, and it is prone to oxidation corrosion and structural collapse during long-term electrochemical cycling, resulting in rapid catalytic performance decay and short service life.

[0004] Therefore, there is an urgent need to provide a method for controlling the synthesis of highly active phases and accurately constructing sheet-like Fe-NC electrocatalysts through pressure field regulation, which can solve the core problems of difficult morphology control, limited active phase regulation, low preparation efficiency, and insufficient exposure of active sites, and simultaneously improve the electrocatalytic performance and industrial adaptability of the catalyst. Summary of the Invention

[0005] The purpose of this invention is to provide a layered Fe-NC electrocatalyst prepared under ultra-high pressure and its preparation method to solve the above-mentioned problems.

[0006] This invention provides a method for preparing a sheet-like Fe-NC electrocatalyst using ultra-high pressure assisted synthesis, comprising the following steps: S1. Mix the iron source, nitrogen-containing organic ligand and hard template in a certain proportion to obtain the precursor complex; S2. Encapsulate the precursor complex in the high-pressure chamber of the high-pressure device; S3. Heat treatment under ultra-high pressure conditions; S4. After depressurization and cooling, the hard template and unstable metal phase are removed by chemical etching to obtain a layered Fe-NC electrocatalyst.

[0007] Preferably, the iron source in S1 is an iron salt or an iron-organic metal complex.

[0008] Preferably, the nitrogen-containing organic ligand in S1 is one or more of the following: 2,4,6-tris(2-pyridyl)-s-triazine, 2,4,6-tris(4-pyridyl)-1,3,5-triazine, 2,4,6-tris(2-pyridyl)pyrimidine, 3,6-bis(2-pyridyl)-1,2,4,5-tetraazine, 1,3,5-tris(2-pyridyl)benzene, 2,4,6-tris(2-pyrimidinyl)-1,3,5-triazine, and 2,3,5,6-tetra(2-pyridyl)pyrazine.

[0009] Preferably, the hard template in S1 is fumed silica, and the mass ratio of the total mass of the iron source and the nitrogen-containing organic ligand to the mass of the hard template is 1:0.5 to 1:5, and the mass ratio of the iron source to the nitrogen-containing organic ligand is 1:1 to 1:10.

[0010] Preferably, the heat treatment under ultra-high pressure in S3 is carried out as follows: the high-pressure device provides a pressure of 1-10 GPa and heats the temperature to 800-1200℃ for heat treatment, holds for 5-120 minutes, and the heating rate is 1-10℃ / min.

[0011] Preferably, the pressure is 3-6 GPa.

[0012] A layered Fe-NC electrocatalyst prepared under ultra-high pressure assistance is disclosed. The layered Fe-NC electrocatalyst is prepared by the above-described preparation method and exhibits an anisotropic two-dimensional sheet morphology with a thickness of 10-100 nm.

[0013] Preferably, the layered Fe-NC electrocatalyst comprises Fe-N, which is unstable under normal pressure. x The active phase, and in 0.1 MkOH electrolyte, has an oxygen reduction half-wave potential E 1 / 2 =0.822V (vs.RHE).

[0014] Therefore, the present invention employs the above-mentioned ultra-high pressure assisted preparation of a layered Fe-NC electrocatalyst and its preparation method, which has the following beneficial effects: (1) The use of ultra-high pressure environment can effectively suppress the structural collapse during the pyrolysis process and controllably prepare two-dimensional sheet-like Fe-NC electrocatalyst. Its through mass transfer channels significantly reduce the mass transfer resistance of the electrochemical reaction and greatly improve the exposure of active sites, providing sufficient active interface for oxygen reduction reaction.

[0015] (2) By controlling the thermodynamic and kinetic pathways of the pyrolysis process under ultra-high pressure, highly active Fe-N with specific electronic spin states that cannot exist under normal pressure can be stably synthesized. x By regulating the electronic structure of the metal active center, the coordination structure significantly enhances the intrinsic catalytic activity of a single active site, achieving a fundamental leap in catalytic performance.

[0016] (3) The solid-phase conversion rate under ultra-high pressure is much higher than that of gas-solid phase reaction under normal pressure. The high-temperature holding time can be shortened from several hours in the existing technology to tens of minutes, which significantly shortens the preparation cycle and reduces production energy consumption. At the same time, the closed high-pressure chamber environment is not affected by airflow disturbance, and the material is heated and pressurized evenly, which can fully ensure the batch uniformity of products in the process of large-scale production.

[0017] (4) The layered carbon matrix treated with ultra-high pressure densification has significantly improved densification, chemical stability and anti-oxidation and anti-corrosion capabilities. It can effectively avoid structural collapse and loss of active sites during long-term electrochemical cycling, greatly improve the cycle stability of the catalyst, and meet the long-term stable service requirements of energy devices such as fuel cells.

[0018] (5) The prepared sheet-like Fe-NC electrocatalyst can reach a half-wave potential of 0.85V (vs. RHE) in 0.1M KOH electrolyte. Its catalytic performance is comparable to that of commercial platinum-based catalysts. It has the core advantages of low cost, high activity and easy scalability, and has extremely high industrial application value.

[0019] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0020] Figure 1 This is a scanning electron microscope (SEM) image of Example 1 of the preparation method of a sheet-like Fe-NC electrocatalyst prepared under ultra-high pressure assistance according to the present invention; Figure 2 This is a scanning electron microscope (SEM) image of a sheet-like Fe-NC electrocatalyst prepared under ultra-high pressure assistance according to the present invention and its preparation method, as shown in Comparative Example 1. Figure 3 The X-ray diffraction (XRD) patterns of Example 1 and Comparative Example 1 of the present invention, which describes a layered Fe-NC electrocatalyst prepared under ultra-high pressure assistance and its preparation method. Detailed Implementation

[0021] To better understand the above technical solutions, a detailed description of the solutions will be provided below in conjunction with the accompanying drawings and specific embodiments. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0022] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a,” “the,” and “the” as used in the embodiments of this invention and the appended claims are also intended to include the plural forms, and “multiple” generally includes at least two unless the context clearly indicates otherwise.

[0023] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that an article or device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or device. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the article or device that includes said element.

[0024] A method for preparing a sheet-like Fe-NC electrocatalyst using ultra-high pressure assisted preparation includes the following steps: S1. Mix an iron source, a nitrogen-containing organic ligand, and a hard template in a certain proportion to obtain a precursor complex; the iron source is an iron salt or an iron-metal organometallic complex; the nitrogen-containing organic ligand is preferably 2,4,6-tris(2-pyridyl)-s-triazine; the hard template is preferably fumed silica, and the total mass ratio of the iron source and the nitrogen-containing organic ligand to the hard template is 1:0.5 to 1:5.

[0025] S2. The precursor composite is encapsulated in the high-pressure chamber of the high-pressure device; specifically, the mixed precursor composite powder is pre-pressed and encapsulated in a gold foil or graphite crucible, and placed in the pyrophyllite pressure chamber of a six-sided press.

[0026] S3. Heat treatment under ultra-high pressure conditions: The high-pressure device provides a pressure of 1-10 GPa and heats the temperature to 800-1200℃ for 5-120 minutes, with a heating rate of 1-10℃ / min. The preferred pressure is 3-6 GPa.

[0027] S4. After depressurization and cooling, the hard template and unstable metal phase are removed by chemical etching. Preferably, the silicon dioxide template is washed away by hydrofluoric acid or hot alkaline solution to obtain a layered Fe-NC electrocatalyst.

[0028] The technical principle of the above preparation method is based on the thermodynamic effects of an ultra-high pressure (GPa level) synthesis environment. According to the thermodynamic equation... The enormous pressure term (VΔP) can forcibly alter the direction of chemical reactions, resulting in multiple key effects: the ultra-high pressure environment significantly reduces interatomic spacing, alters the hybrid orbital evolution path of carbon atoms, and simultaneously suppresses the disordered expansion of the carbon matrix at high temperatures; combined with the confinement effect of the SiO2 hard template, the pressure field guides the carbon matrix to preferentially grow along a two-dimensional direction, obtaining a lamellar morphology. High pressure conditions effectively suppress excessive nitrogen loss and significantly shorten interatomic spacing, increasing the solid solubility of iron atoms in the nitrogen-doped carbon matrix, thereby forming high-density Fe-N4 active centers and promoting the graphitization degree of carbon materials. This strategy can obtain high-density, asymmetric coordination phases that are difficult to synthesize under normal pressure.

[0029] The layered Fe-NC electrocatalysts prepared by the above method exhibit anisotropic two-dimensional sheet morphology with a thickness of 10-100 nm. The layered Fe-NC electrocatalysts contain Fe-N atoms that are unstable under ambient pressure. x The active phase, and in 0.1M KOH electrolyte, has an oxygen reduction half-wave potential E 1 / 2 =0.85V (vs.RHE).

[0030] To more clearly and in detail introduce the ultra-high pressure assisted preparation of a layered Fe-NC electrocatalyst and its preparation method provided in the embodiments of the present invention, the following description will be based on specific embodiments.

[0031] Example 1 A method for preparing a layered Fe-NC catalyst, the specific steps of which are as follows: Precursor construction: Fe-TPTZ complex was prepared by mixing ferrous acetate source with 2,4,6-tris(2-pyridyl)-s-triazine at a mass ratio of 1:5; Fe-TPTZ complex was then thoroughly ground and mixed with fumed silica hard template at a mass ratio of 1:1 to obtain a uniformly mixed precursor complex powder.

[0032] Ultra-high pressure loading: The above-mentioned precursor composite powder is pre-pressed and encapsulated in a high-purity graphite crucible, and then the crucible is placed in the pyrophyllite pressure chamber of a six-sided top press to complete the high-pressure transmission and sealing assembly.

[0033] High-pressure heat treatment: Apply 5GPa ultra-high pressure to the cavity using a six-sided top press. After the pressure stabilizes, rapidly heat up to 1000℃ at a rate of 10℃ / min, and maintain the temperature and pressure for 30 minutes. After the treatment, stop heating and allow the cavity to cool naturally to room temperature.

[0034] Post-processing: After depressurization, the sample was taken out and soaked in a 10% hydrofluoric acid solution for 24 hours to remove the silica hard template. After washing with deionized water until neutral, it was vacuum dried to finally obtain the layered Fe-NC electrocatalyst.

[0035] Characterized by SEM, such as Figure 1 As shown, the electrocatalyst prepared in this embodiment exhibits a uniform two-dimensional sheet structure with a sheet thickness concentrated in the range of 20-50 nm. There is no obvious agglomeration, and abundant interconnected channels are formed between the sheets.

[0036] Comparative Example 1 This comparative example serves as a blank control for Example 1. Only the heat treatment process is conducted under normal pressure; the remaining raw material ratios, precursor preparation, and post-treatment processes are completely identical to those in Example 1. The specific steps are as follows: Precursor construction: Same as in Example 1, to prepare a precursor composite powder of Fe-TPTZ complex and fumed silica.

[0037] Atmospheric pressure charging: Place the precursor compound powder in a corundum ceramic boat and put it into the constant temperature zone of an atmospheric pressure tube furnace.

[0038] Atmospheric pressure heat treatment: High-purity nitrogen is continuously introduced into the tube furnace as a protective atmosphere. After the atmosphere is replaced, the temperature is raised to 1000℃ at a rate of 5℃ / min and held for 2 hours. After the treatment, heating is stopped and the furnace is allowed to cool naturally to room temperature under a nitrogen atmosphere.

[0039] Post-processing: The sample was removed and subjected to the same hydrofluoric acid template removal, washing and drying process as in Example 1 to obtain the comparative Fe-NC electrocatalyst.

[0040] The products prepared in this comparative example were mostly irregular blocky aggregates, lacking obvious two-dimensional lamellar structures, and exhibiting severe aggregation and pore collapse phenomena, such as... Figure 2 As shown.

[0041] Systematic characterization and performance testing were conducted on the samples from Example 1 and Comparative Example 1. The core comparison results are as follows: The Fe-NC electrocatalysts obtained in Example 1 and Comparative Example 1 were characterized by SEM. The results showed that: Example 1 effectively suppressed the structural collapse and particle agglomeration caused by the decomposition of organic matter during pyrolysis under ultra-high pressure environment, and successfully constructed a uniform two-dimensional sheet structure with a thickness of 20-50 nm, forming abundant through mass transfer channels and fully exposing catalytic active sites; while the atmospheric pressure pyrolysis product of Comparative Example 1 showed severe structural collapse and particle agglomeration, no ordered sheet structure, severe pore closure, and a large number of active sites were buried.

[0042] ORR performance was tested in a three-electrode system with 0.1M KOH electrolyte. The results showed that the catalyst prepared in Example 1 had a half-wave potential of 0.822V (vs. RHE), and its catalytic performance was basically the same as that of the commercial 20% Pt / C catalyst. However, the half-wave potential of the sample in Comparative Example 1 at atmospheric pressure was only 0.764V (vs. RHE), and its catalytic performance was much lower than that of Example 1. It can be seen that the ultra-high pressure preparation scheme of Example 1 can significantly improve the electrocatalytic activity of Fe-NC catalyst.

[0043] The crystalline phase composition and active phase structure of the electrocatalysts prepared in Example 1 and Comparative Example 1 were characterized by X-ray diffraction (XRD). The results showed that, in addition to the characteristic diffraction peaks of the carbon matrix, the ultra-high pressure prepared sample of Example 1 exhibited several characteristic diffraction peaks not present in the atmospheric pressure pyrolysis sample. These peaks correspond to highly active metastable Fe-N, which is stably generated under ultra-high pressure and is difficult to synthesize or even exist under atmospheric pressure thermodynamic conditions. x The coordination crystal phase confirms that this invention successfully overcomes the limitations of ambient pressure thermodynamic conditions by controlling the thermodynamic and kinetic pathways of the pyrolysis process through an ultra-high pressure field, achieving the controllable synthesis of highly intrinsically active phases. The intrinsic catalytic activity of single active sites can be significantly enhanced by controlling the electronic spin state and electronic structure of the metal active center. In contrast, the ambient pressure pyrolysis sample of Comparative Example 1 only showed characteristic diffraction peaks of the carbon matrix and conventionally thermodynamically stable iron-based compounds, without the highly active metastable Fe-N phase. x The characteristic signals of the coordination phase cannot overcome the inherent bottleneck of phase regulation under normal pressure, and the intrinsic catalytic activity of its active sites is far lower than that of the ultra-high pressure prepared sample in Example 1.

[0044] The preparation processes of Example 1 and Comparative Example 1 show that the high-temperature holding time in Example 1 is only 30 minutes, which is 75% shorter than the 2-hour holding time of atmospheric pressure pyrolysis in Comparative Example 1. Simultaneously, the ultra-high pressure rapid heating heat treatment mode significantly reduces energy consumption in the high-temperature section, resulting in a lower overall production energy consumption compared to Comparative Example 1. Furthermore, the heat treatment environment of the sealed high-pressure chamber is unaffected by airflow disturbances, and the batch uniformity of the products is far superior to that of the atmospheric pressure tube furnace process, making it more suitable for industrial-scale production.

[0045] Therefore, this invention employs the aforementioned ultra-high pressure assisted preparation of a layered Fe-NC electrocatalyst and its preparation method. The ultra-high pressure environment effectively suppresses structural collapse during pyrolysis, allowing for the controllable preparation of a two-dimensional layered Fe-NC electrocatalyst. Its interconnected mass transfer channels significantly reduce the mass transfer resistance of the electrochemical reaction, while simultaneously greatly increasing the exposure of active sites, providing ample active interfaces for the oxygen reduction reaction. By controlling the thermodynamic and kinetic pathways of the pyrolysis process through an ultra-high pressure field, highly active Fe-NC electrocatalysts with specific electronic spin states, which cannot exist under normal pressure, can be stably synthesized. x By regulating the electronic structure of the metal active center, the coordination structure significantly enhances the intrinsic catalytic activity of a single active site, achieving a fundamental leap in catalytic performance.

[0046] The solid-phase conversion rate under ultra-high pressure is much higher than that under normal pressure, reducing the high-temperature holding time from several hours to tens of minutes, significantly shortening the preparation cycle and reducing production energy consumption. Simultaneously, the sealed high-pressure chamber environment is unaffected by airflow disturbances, ensuring uniform heating and pressure application of the material and guaranteeing batch-to-batch uniformity in large-scale production. The layered carbon matrix, densified under ultra-high pressure, exhibits significantly improved density, chemical stability, and antioxidant and corrosion resistance, effectively preventing structural collapse and loss of active sites during long-term electrochemical cycling. This greatly enhances the catalyst's cycle stability, meeting the long-term stable service requirements of energy devices such as fuel cells.

[0047] The prepared sheet-like Fe-NC electrocatalyst can achieve a half-wave potential of 0.85V (vs. RHE) in 0.1M KOH electrolyte, and its catalytic performance is comparable to that of commercial platinum-based catalysts. It has the core advantages of low cost, high activity and easy scalability, and has extremely high industrial application value.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a layered Fe-NC electrocatalyst using ultra-high pressure assisted preparation, characterized in that, Includes the following steps: S1. Mix the iron source, nitrogen-containing organic ligand and hard template in a certain proportion to obtain the precursor complex; S2. Encapsulate the precursor complex in the high-pressure chamber of the high-pressure device; S3. Heat treatment under ultra-high pressure conditions; S4. After depressurization and cooling, the hard template and unstable metal phase are removed by chemical etching to obtain a layered Fe-NC electrocatalyst.

2. The method for preparing a layered Fe-NC electrocatalyst using ultra-high pressure assisted preparation according to claim 1, characterized in that, The iron source mentioned in S1 is an iron salt or an iron-organic metal complex.

3. The method for preparing a layered Fe-NC electrocatalyst using ultra-high pressure assisted preparation according to claim 1, characterized in that, The nitrogen-containing organic ligand described in S1 is one or more of the following: 2,4,6-tris(2-pyridyl)-s-triazine, 2,4,6-tris(4-pyridyl)-1,3,5-triazine, 2,4,6-tris(2-pyridyl)pyrimidine, 3,6-bis(2-pyridyl)-1,2,4,5-tetraazine, 1,3,5-tris(2-pyridyl)benzene, 2,4,6-tris(2-pyrimidinyl)-1,3,5-triazine, and 2,3,5,6-tetra(2-pyridyl)pyrazine.

4. The method for preparing a layered Fe-NC electrocatalyst using ultra-high pressure assisted preparation according to claim 1, characterized in that, The hard template described in S1 is fumed silica, and the total mass ratio of the iron source and the nitrogen-containing organic ligand to the hard template is 1:0.5 to 1:5, and the mass ratio of the iron source to the nitrogen-containing organic ligand is 1:1 to 1:

10.

5. The method for preparing a layered Fe-NC electrocatalyst using ultra-high pressure assisted preparation according to claim 1, characterized in that, The heat treatment under ultra-high pressure conditions in S3 is carried out as follows: the high-pressure device provides a pressure of 1-10 GPa and heats the temperature to 800-1200℃ for heat treatment, holding for 5-120 minutes, with a heating rate of 1-10℃ / min.

6. The method for preparing a layered Fe-NC electrocatalyst using ultra-high pressure assisted preparation according to claim 5, characterized in that, The pressure is 3-6 GPa.

7. A layered Fe-NC electrocatalyst prepared under ultra-high pressure, characterized in that, The layered Fe-NC electrocatalyst is prepared by the preparation method according to any one of claims 1-6, and the layered Fe-NC electrocatalyst exhibits anisotropic two-dimensional sheet morphology with a thickness of 10-100 nm.

8. The layered Fe-NC electrocatalyst prepared under ultra-high pressure assistance according to claim 7, characterized in that, The layered Fe-NC electrocatalyst contains Fe-N, which is unstable under normal pressure. x The active phase, and in 0.1M KOH electrolyte, has an oxygen reduction half-wave potential E 1 / 2 =0.822V (vs.RHE).

Images