Inorganic salt-assisted derived from supported fe-n-c oxygen reduction electrocatalysts and methods of making the same

Abstract

This invention discloses an inorganic salt-assisted self-supported Fe-N-C oxygen reduction electrocatalyst and its preparation method. The electrocatalyst is an irregular particle and / or plate-like aggregate; the C element content is 82.64-90.64 at.%, the N element content is 2.95-5.95 at.%, the Fe element content is 0.06-0.28 at.%, the average mesopore diameter is 9.7±0.2 nm, the most probable pore diameter is 2.1 nm, and the specific surface area is 1124±5 m². 2 g ‑1 The self-supported Fe-N-C oxygen reduction catalyst includes a nitrogen-containing precursor, a nitrogen-doped agent, a pore-forming agent, and a nitrogen-containing precursor molecular structure regulator. The nitrogen-containing precursor includes polyaniline, and the nitrogen-containing precursor molecular structure regulator includes inorganic salts. The mass ratio of the nitrogen-containing precursor to the nitrogen-doped agent is 2:1 to 20. The electrocatalyst and its preparation method of this invention have the advantages of inexpensive and readily available raw materials, simple and controllable process, and excellent electrochemical performance.

Description

Technical Field

[0001] This invention relates to the field of non-precious metal catalyst technology, specifically to an inorganic salt-assisted self-supported Fe-NC oxygen reduction electrocatalyst and its preparation method. Background Technology

[0002] Currently, Fe-NC materials exhibit activity comparable to or even exceeding that of commercial Pt / C catalysts in three-electrode systems for catalyzing the oxygen reduction reaction (ORR), and are considered one of the most promising non-precious metal catalysts to replace the noble metal Pt in fuel cell cathode ORR. Nevertheless, further increasing the active site density of Fe-NC catalysts to enhance their activity and stability still faces significant challenges.

[0003] Fe-NC materials synthesized using mesoporous silica as hard templates exhibit significant activity and stability for ORR; Fe-NC materials created using metal-organic frameworks (MOFs) as carbon and nitrogen precursors and through precise design of local coordination environments also demonstrate very high ORR activity. The results show that the Fe-NC materials obtained by the above strategies do indeed have a higher active site density than Fe-NC materials synthesized by conventional methods, thus exhibiting superior electrocatalytic performance. Nevertheless, some of these methods have high raw material costs. For example, Chinese invention patent application CN110137518A mainly uses self-made mesoporous molecular sieves and chelating agent sodium ethylenediaminetetraacetate as raw materials. Chinese invention patent application CN113368879A mainly uses multi-toothed chelating agents as raw materials. Some require corrosive acids or strong bases to etch away the hard template, which increases energy consumption. For example, Chinese invention patent application CN110137518A requires etching with an acid or base ethanol aqueous solution in step 3) of its preparation. Chinese invention patent application CN113368879A requires etching with an acid or base ethanol aqueous solution in step S3 to obtain the primary catalyst with removed silica microspheres.

[0004] The above defects will significantly increase the production cost of Fe-NC materials, making it impossible to meet the demand for inexpensive and high-performance Fe-NC catalysts. Summary of the Invention

[0005] The purpose of this invention is to provide an inorganic salt-assisted derived self-supported Fe-NC oxygen reduction electrocatalyst and its preparation method, which has the characteristics of inexpensive and readily available raw materials, simple and controllable process, and excellent electrochemical performance.

[0006] This invention can be achieved through the following technical solutions:

[0007] This invention discloses an inorganic salt-assisted derived self-supported Fe-NC oxygen reduction electrocatalyst, wherein the self-supported Fe-NC oxygen reduction catalyst is an irregular particle and / or plate-like aggregate;

[0008] The carbon content is 82.64-90.64 at.%, the nitrogen content is 2.95-5.95 at.%, and the fe content is 0.06-0.28 at.%. The average mesopore size is 9.7 ± 0.2 nm, the most probable pore size is 2.1 nm, and the specific surface area is 1124 ± 5 ​​m². 2 g -1 ;

[0009] The self-supported Fe-NC oxygen reduction catalyst includes a nitrogen-containing precursor, a nitrogen-doping agent, a pore-forming agent, and a nitrogen-containing precursor molecular structure regulator. The nitrogen-containing precursor includes polyaniline, and the nitrogen-containing precursor molecular structure regulator includes inorganic salts. The mass ratio of the nitrogen-containing precursor to the nitrogen-doped agent is 2:1 to 20.

[0010] Furthermore, the nitrogen-containing precursor is one or a combination of two or more of polyaniline, polypyrrole, poly(o-phenylenediamine) and / or polydopamine.

[0011] Furthermore, the nitrogen-doped auxiliaries and pore-forming agents are one or more of melamine, cyanamide, urea, and / or ammonium chloride.

[0012] Furthermore, the inorganic salt is one or a combination of two or more of AlCl3, NaF, NaCl, NaBr, NaI, KCl, MgCl2 and / or NH4Cl.

[0013] Another aspect of the present invention relates to a method for preparing the above-mentioned inorganic salt-assisted derived self-supported Fe-NC oxygen reduction electrocatalyst, comprising the following steps:

[0014] S1. Preparation of solid powder A: First, an inorganic salt, which serves as a molecular structure regulator for nitrogen-containing precursors, is added to an acidic aqueous solution. Then, the monomer of the nitrogen-containing precursor is added and ultrasonically dispersed evenly. Next, an aqueous solution of ammonium persulfate and FeCl3·6H2O is added dropwise and stirred continuously. Finally, the above mixed solution is filtered, dried, and ground to obtain solid powder A.

[0015] S2. Preparation of catalyst precursor: A obtained in step S1 is mixed with melamine, which is used as a nitrogen-doped auxiliary agent and pore-forming agent, in a solid phase to obtain the catalyst precursor.

[0016] S3. Preparation of primary catalyst: The B obtained in step S2 is heated to 850-950℃ at 10±5℃ / min and held for 1-3h under the protection of flowing inert gas. Then it is naturally cooled to room temperature and ground uniformly to obtain the primary catalyst.

[0017] S4. Acid treatment of the catalyst: The primary catalyst obtained in step 3) is impregnated in an acid solution of 0.5-2M at 60-80℃ and stirred for 0.5-24h. After the treatment, it is filtered, washed and dried to obtain a self-supported Fe-NC catalyst with some iron species removed.

[0018] S5. Secondary heat treatment of the catalyst: The self-supported Fe-NC catalyst obtained in step S4 is subjected to heat treatment at 180–220 mL / min. -1 Under the protection of flowing gas, the temperature is increased to 800-1000℃ at 10±5℃ / min and held for 0.5-3h, and then naturally cooled to room temperature to obtain the final self-supported Fe-NC oxygen reduction catalyst.

[0019] Further, in step S2, solid-phase mixing is solid-phase grinding and / or ball milling mixing.

[0020] Furthermore, in step S3, the flowing inert gas is nitrogen and / or argon.

[0021] Furthermore, in step S5, the flowing gas is nitrogen and / or argon.

[0022] This invention discloses an inorganic salt-assisted derived self-supported Fe-NC oxygen reduction electrocatalyst and its preparation method, which has the following beneficial effects:

[0023] First, the raw materials are cheap and readily available. The preparation process uses cheap polyaniline (PANI) and its similar structural polymers, melamine (MA) and sodium chloride as nitrogen-containing precursor, nitrogen-doped auxiliaries (which also act as pore-forming agents) and inorganic salt regulators, respectively.

[0024] Secondly, the process is simple and controllable. Since no additional hard template is used in the preparation process, no etching is required. In addition, by adding inorganic salts during the oxidative polymerization of aniline into PANI or similar structures, and then mixing it with MA in a solid phase and then thermally decomposing it, the degree of N doping can be effectively improved, creating a rich micro-meso-level pore structure, large mesopore diameter and very high specific surface area, and forming highly dispersed Fe species. This exposes more active sites and improves their utilization rate, while providing a fast transport channel for matter and electrons in the ORR process.

[0025] Third, it exhibits excellent electrochemical performance. Under alkaline conditions, the activity (initial potential, half-wave potential, and kinetic current density at high potential) of this self-supported hierarchical porous Fe-NC material in catalyzing ORR, its methanol resistance, and operational stability are significantly higher than those of commercial Pt / C catalysts, and it also achieves high energy conversion efficiency with 4e - The reaction pathway catalyzes the production of water from ORR;

[0026] Fourth, it has broad application prospects. This catalyst has a wide range of applications and can be used as a cathode oxygen reduction catalyst for various batteries. Attached Figure Description

[0027] Figure 1 PANI / MA 0.5 -Fe (SC) - TEM image, HAADF and elemental mapping image of HT2.

[0028] Figure 2 PANI / MA 0.5 -Fe (SC) XRD pattern of -HT2.

[0029] Figure 3 PANI / MA 0.5 -Fe (SC) Raman spectrum of -HT2.

[0030] Figure 4 PANI / MA 0.5 -Fe (SC) -HT2 XPS full spectrum.

[0031] Figure 5 PANI / MA 0.5 -Fe (SC) -N2 adsorption / desorption isotherms and pore size distribution of HT2.

[0032] Figure 6 PANI / MA 0.5 -Fe-HT2, PANI-Fe (SC) -HT2, PANI / MA 0.5 -Fe (SC) Polarization curves of ORR catalyzed by -HT2 and Pt / C in O2-saturated 0.1M KOH (room temperature, scan rate 10 mV s) -1 (Speed: 1600 rpm).

[0033] Figure 7 PANI / MA at different rotation speeds 0.5 -Fe (SC) -Polarization curves of ORR catalyzed by HT2 and the number of electrons transferred per O2 molecule under different potentials.

[0034] Figure 8 PANI / MA 0.5 -Fe (SC) -Methanol resistance of HT2 and Pt / C at 0.57V.

[0035] Figure 9 PANI / MA 0.5-Fe (SC) -Methanol resistance of HT2 and Pt / C at 0.85V.

[0036] Figure 10 PANI / MA 0.5 -Fe (SC) -Stability of ORR catalyzed by HT2. Detailed Implementation

[0037] To enable those skilled in the art to better understand the technical solution of the present invention, the product of the present invention will be further described in detail below with reference to embodiments and accompanying drawings.

[0038] This invention discloses an inorganic salt-assisted derived self-supported Fe-NC oxygen reduction electrocatalyst, wherein the self-supported Fe-NC oxygen reduction catalyst is an irregular particle and / or plate-like aggregate;

[0039] The carbon content is 82.64-90.64 at.%, the nitrogen content is 2.95-5.95 at.%, and the fe content is 0.06-0.28 at.%. The average mesopore size is 9.7 ± 0.2 nm, the most probable pore size is 2.1 nm, and the specific surface area is 1124 ± 5 ​​m². 2 g -1 ;

[0040] The self-supported Fe-NC oxygen reduction catalyst includes a nitrogen-containing precursor, a nitrogen-doping agent, a pore-forming agent, and a nitrogen-containing precursor molecular structure regulator. The nitrogen-containing precursor includes polyaniline, and the nitrogen-containing precursor molecular structure regulator includes inorganic salts. The mass ratio of the nitrogen-containing precursor to the nitrogen-doped agent is 2:1 to 20.

[0041] Furthermore, the nitrogen-containing precursor is one or a combination of two or more of polyaniline, polypyrrole, poly(o-phenylenediamine) and / or polydopamine.

[0042] Furthermore, the nitrogen-doped auxiliaries and pore-forming agents are one or more of melamine, cyanamide, urea, and / or ammonium chloride.

[0043] Furthermore, the inorganic salt is one or a combination of two or more of AlCl3, NaF, NaCl, NaBr, NaI, KCl, MgCl2 and / or NH4Cl.

[0044] Another aspect of the present invention relates to a method for preparing the above-mentioned inorganic salt-assisted derived self-supported Fe-NC oxygen reduction electrocatalyst, comprising the following steps:

[0045] S1. Preparation of solid powder A: First, an inorganic salt, which serves as a molecular structure regulator for nitrogen-containing precursors, is added to an acidic aqueous solution. Then, the monomer of the nitrogen-containing precursor is added and ultrasonically dispersed evenly. Next, an aqueous solution of ammonium persulfate and FeCl3·6H2O is added dropwise and stirred continuously. Finally, the above mixed solution is filtered, dried, and ground to obtain solid powder A.

[0046] S2. Preparation of catalyst precursor: A obtained in step S1 is mixed with melamine, which is used as a nitrogen-doped auxiliary agent and pore-forming agent, in a solid phase to obtain the catalyst precursor.

[0047] S3. Preparation of primary catalyst: The B obtained in step S2 is heated to 850-950℃ at 10±5℃ / min and held for 1-3h under the protection of flowing inert gas. Then it is naturally cooled to room temperature and ground uniformly to obtain the primary catalyst.

[0048] S4. Acid treatment of the catalyst: The primary catalyst obtained in step 3) is impregnated in an acid solution of 0.5-2M at 60-80℃ and stirred for 0.5-24h. After the treatment, it is filtered, washed and dried to obtain a self-supported Fe-NC catalyst with some iron species removed.

[0049] S5. Secondary heat treatment of the catalyst: The self-supported Fe-NC catalyst obtained in step S4 is subjected to heat treatment at 180–220 mL / min. -1 Under the protection of flowing gas, the temperature is increased to 800-1000℃ at 10±5℃ / min and held for 0.5-3h, and then naturally cooled to room temperature to obtain the final self-supported Fe-NC oxygen reduction catalyst.

[0050] Further, in step S2, solid-phase mixing is solid-phase grinding and / or ball milling mixing.

[0051] Furthermore, in step S3, the flowing inert gas is nitrogen and / or argon.

[0052] Furthermore, in step S5, the flowing gas is nitrogen and / or argon.

[0053] The activity of Fe-NC materials in electrocatalytic ORR depends on their active site density and utilization rate, which are largely affected by the precursor structure, the interaction of various precursors during the preparation process, and the texture properties (pore structure, pore size, specific surface area) of the final material.

[0054] This invention does not introduce an additional carbon support, but only uses polyaniline (PANI) and its similar structural polymers as nitrogen-containing precursors for high-temperature pyrolysis. This self-doping is expected to obtain a more uniform distribution of nitrogen-related active sites and increase their density. Simultaneously, melamine (MA) is used as a nitrogen-doping agent. The purpose is to utilize the abundant nitrogen content of MA to increase the degree of nitrogen doping. Another purpose is to utilize the gas generated during the thermal pyrolysis of MA to form a hierarchical porous structure in the carbon material obtained by carbonizing PANI or similar structures (because MA has a lower degradation temperature than PANI, the generated gas can create pores during escape). This also results in a large specific surface area, which is beneficial for the exposure of active sites, improved utilization of active sites, and mass transfer and diffusion of substrate products, thereby increasing the electron transfer rate. Introducing inorganic salts during the oxidative polymerization of nitrogen-containing precursor monomers into PANI or its similar structural polymers aims to change the ionic strength of the solution, thus altering the polymerization rate and growth direction of PANI and its similar structural polymers. This optimizes the PANI molecular structure to obtain high FeN... x The high density of active sites, high total utilization of active sites, and hierarchical pore structure lead to the synergistic development of non-noble metal catalysts with excellent ORR activity.

[0055] The method described in this invention, which uses polyaniline (PANI) and similar structures and melamine (MA) as nitrogen-containing precursors and nitrogen-doping additives respectively, and derives a self-supported Fe-NC catalyst by means of inorganic salt action, requires low-cost raw materials, has low reagent toxicity, is safe and environmentally friendly, is simple and controllable, has a large space for process optimization, has high material productivity, and is easy to scale up for production.

[0056] Example 1

[0057] 1) Add 2 mL of aniline to a 0.5 M HCl solution. After ultrasonic dispersion for about 1 h, keep the temperature below 10 °C and add a certain amount of 1 M ammonium persulfate dropwise while stirring continuously. After about 0.5 h, add 5 mL of FeCl3·6H2O aqueous solution dropwise and continue stirring for 24 h to allow aniline to be fully oxidized and polymerized into PANI. Then, filter, evaporate and dry the mixture in sequence.

[0058] 2) Add 0.5g of melamine (MA) to the above mixture, mix in the solid phase, and grind evenly.

[0059] 3) Spread the above solid powder evenly in a quartz boat and place it in a tube furnace, heating at 200 mL / min. -1 Under N2 purging, the temperature is increased to 900℃ at 10℃ / min and maintained for 1 hour, then naturally cooled to room temperature, and then ground uniformly. The product at this stage is named PANI / MA. 0.5 -Fe-HT1.

[0060] 4) PANI / MA 0.5 -Fe-HT1 was added to a 30 mL 0.5 M H2SO4 solution at 60 °C for acid treatment for 8 hours. After treatment, the solution was filtered, washed, and dried. The product at this stage was named PANI / MA. 0.5 -Fe-AL.

[0061] 5) Take 0.15g PANI / MA 0.5 -Fe-AL in 200mL min -1 Under N2 protection, the temperature was increased to 900℃ at a rate of 10℃ / min and held for 1 hour, then allowed to cool naturally to room temperature. After grinding evenly, the sample was ready for use. The sample obtained in this stage was labeled PANI / MA. 0.5 -Fe-HT2.

[0062] This preparation process did not use inorganic salt NaCl as an activator, but used MA as a nitrogen doping aid. It will be used as a control catalyst and compared with the catalyst prepared below that used inorganic salt NaCl as an activator and MA as a nitrogen doping aid.

[0063] Example 2

[0064] 1) Take 0.4g NaCl and 2mL aniline and add them to 0.5M HCl solution. After ultrasonic dispersion (~1h), keep below 10℃ and add a certain amount of 1M ammonium persulfate dropwise while stirring continuously. After about 0.5h, add 5mL of FeCl3·6H2O aqueous solution dropwise and continue stirring for 24h to allow aniline to be fully oxidized and polymerized into PANI. Then, filter, evaporate and dry the above mixture in sequence.

[0065] 2) Spread the above solid powder evenly in a quartz boat and place it in a tube furnace, heating at 200 mL / min. -1 Under N2 purging, the temperature was increased to 900℃ at 10℃ / min and held for 1 hour, then allowed to cool naturally to room temperature. The material was then ground uniformly. The product at this stage was named PANI-Fe. (SC) -HT1.

[0066] 3) PANI-Fe (SC) -HT1 was added to 30 mL of 0.5 M H2SO4 solution at 60 °C for acid treatment for 8 hours. After treatment, the solution was filtered, washed, and dried. The product at this stage was named PANI-Fe. (SC) -AL.

[0067] 4) Take 0.15g PANI-Fe (SC) -AL at 200mL min -1Under N2 protection, the temperature was increased to 900℃ at a rate of 10℃ / min and held for 1 hour, then allowed to cool naturally to room temperature. After grinding evenly, the sample was ready for use. The sample obtained in this stage was labeled as PANI-Fe. (SC) -HT2.

[0068] This preparation process incorporates inorganic salt NaCl as an activator, but does not use MA as a nitrogen-doping aid. It will serve as a control catalyst for comparison with the catalyst prepared below, which incorporates inorganic salt NaCl as an activator and uses MA as a nitrogen-doping aid.

[0069] Example 3

[0070] The experimental procedure was the same as in Example 1, except that 0.4 g of NaCl was added before adding 2 mL of aniline in experimental step 1). The final sample was named PANI / MA. 0.5 -Fe (SC) -HT2.

[0071] The PANI / MA synthesized in this embodiment 0.5 -Fe (SC) The TEM image, XRD pattern, Raman spectrum, XPS pattern, N2 adsorption / desorption isotherm, pore size distribution, and texture parameters of -HT2 are as follows: Figure 1 , 2 As shown in 3, 4, 5 and Table 1.

[0072] Example 4

[0073] A self-supported Fe-NC oxygen reduction catalyst was prepared by the following method:

[0074] 1) Take 0.8g NaCl and 2mL aniline and add them to 0.5M HCl solution. After ultrasonic dispersion (~1h), keep below 10℃ and add a certain amount of 1M ammonium persulfate dropwise while stirring continuously. After about 0.5h, add 5mL of FeCl3·6H2O aqueous solution dropwise and continue stirring for 24h to allow aniline to be fully oxidized and polymerized into PANI. Then, filter, evaporate and dry the above mixture in sequence.

[0075] 2) Add 0.5g of melamine (MA) to the above mixture, mix in the solid phase, and grind evenly.

[0076] 3) Spread the above solid powder evenly in a quartz boat and place it in a tube furnace, heating at 200 mL / min. -1 Under N2 purging, the temperature is increased to 900℃ at 10℃ / min and maintained for 1 hour, then naturally cooled to room temperature, and then ground uniformly. The product at this stage is named PANI / MA. 0.5 -Fe (SC0.8) -HT1.

[0077] 4) PANI / MA 0.5 -Fe (SC0.8) -HT1 was added to 30 mL of 0.5 M H2SO4 solution at 60 °C for acid treatment for 8 hours. After treatment, the solution was filtered, washed, and dried. The product at this stage was named PANI / MA. 0.5 -Fe (SC0.8) -AL.

[0078] 5) Take 0.15g PANI / MA 0.5 -Fe (SC0.8) -AL at 200mL min -1 Under N2 protection, the temperature was increased to 900℃ at a rate of 10℃ / min and held for 1 hour, then allowed to cool naturally to room temperature. After grinding evenly, the sample was ready for use. The sample obtained in this stage was labeled PANI / MA. 0.5 -Fe (SC0.8) -HT2.

[0079] Example 5

[0080] A self-supported Fe-NC oxygen reduction catalyst was prepared by the following method:

[0081] 1) Take 0.4g NaCl and 2mL aniline and add them to 0.5M HCl solution. After ultrasonic dispersion (~1h), keep below 10℃ and add a certain amount of 1M ammonium persulfate dropwise while stirring continuously. After about 0.5h, add 5mL of FeCl3·6H2O aqueous solution dropwise and continue stirring for 24h to allow aniline to be fully oxidized and polymerized into PANI. Then, filter, evaporate and dry the above mixture in sequence.

[0082] 2) Add 1.0g of melamine (MA) to the above mixture, mix in the solid phase, and grind evenly.

[0083] 3) Spread the above solid powder evenly in a quartz boat and place it in a tube furnace, heating at 200 mL / min. -1 Under N2 purging, the temperature is increased to 900℃ at 10℃ / min and maintained for 1 hour, then naturally cooled to room temperature, and then ground uniformly. The product at this stage is named PANI / MA. 1.0 -Fe (SC) -HT1.

[0084] 4) PANI / MA 1.0 -Fe (SC) -HT1 was added to 30 mL of 0.5 M H2SO4 solution at 60 °C for acid treatment for 8 hours. After treatment, the solution was filtered, washed, and dried. The product at this stage was named PANI / MA. 1.0 -Fe (SC)-AL.

[0085] 5) Take 0.15g PANI / MA 1.0 -Fe (SC) -AL at 200mL min -1 Under N2 protection, the temperature was increased to 900℃ at a rate of 10℃ / min and held for 1 hour, then allowed to cool naturally to room temperature. After grinding evenly, the sample was ready for use. The sample obtained in this stage was labeled PANI / MA. 1.0 -Fe (SC) -HT2.

[0086] Example 6

[0087] A self-supported Fe-NC oxygen reduction catalyst was prepared by the following method:

[0088] 1) Take 0.4g NaF and 2mL aniline and add them to 0.5M HCl solution. After ultrasonic dispersion (~1h), keep below 10℃ and add a certain amount of 1M ammonium persulfate dropwise while stirring continuously. After about 0.5h, add 5mL of FeCl3·6H2O aqueous solution dropwise and continue stirring for 24h to allow aniline to be fully oxidized and polymerized into PANI. Then, filter, evaporate and dry the above mixture in sequence.

[0089] 2) Add 0.5g of melamine (MA) to the above mixture, mix in the solid phase, and grind evenly.

[0090] 3) Spread the above solid powder evenly in a quartz boat and place it in a tube furnace, heating at 200 mL / min. -1 Under N2 purging, the temperature is increased to 900℃ at 10℃ / min and maintained for 1 hour, then naturally cooled to room temperature, and then ground uniformly. The product at this stage is named PANI / MA. 0.5 -Fe (SF) -HT1.

[0091] 4) PANI / MA 0.5 -Fe (SF) -HT1 was added to 30 mL of 0.5 M H2SO4 solution at 60 °C for acid treatment for 8 hours. After treatment, the solution was filtered, washed, and dried. The product at this stage was named PANI / MA. 0.5 -Fe (SF) -AL.

[0092] 5) Take 0.15g PANI / MA 0.5 -Fe (SF) -AL at 200mL min -1Under N2 protection, the temperature was increased to 900℃ at a rate of 10℃ / min and held for 1 hour, then allowed to cool naturally to room temperature. After grinding evenly, the sample was ready for use. The sample obtained in this stage was labeled PANI / MA. 0.5 -Fe (SF) -HT2.

[0093] Example 7

[0094] A self-supported Fe-NC oxygen reduction catalyst was prepared by the following method:

[0095] 1) Take 0.4g NaCl and 2mL aniline and add them to a 0.5M dodecylbenzenesulfonic acid solution. After ultrasonic dispersion for about 1h, keep the temperature below 10℃ and add a certain amount of 1M ammonium persulfate dropwise while stirring continuously. After about 0.5h, add 5mL of FeCl3·6H2O aqueous solution dropwise and continue stirring for 24h to allow aniline to be fully oxidized and polymerized into PANI. Then, filter, evaporate and dry the mixture in sequence.

[0096] 2) Add 0.5g of melamine (MA) to the above mixture, mix in the solid phase, and grind evenly.

[0097] 3) Spread the above solid powder evenly in a quartz boat and place it in a tube furnace, heating at 200 mL / min. -1 Under N2 purging, the temperature is increased to 900℃ at 10℃ / min and maintained for 1 hour, then naturally cooled to room temperature, and then ground uniformly. The product at this stage is named PANI. DBSA / MA 0.5 -Fe (SC) -HT1.

[0098] 4) Place PANI DBSA / MA 0.5 -Fe (SC) -HT1 was added to a 30 mL 0.5 M H2SO4 solution at 60 °C for acid treatment for 8 hours. After treatment, the solution was filtered, washed, and dried. The product at this stage was named PANI. DBSA / MA 0.5 -Fe (SC) -AL.

[0099] 5) Take 0.15g PANI DBSA / MA 0.5 -Fe (SC) -AL at 200mL min -1 Under N2 protection, the temperature was increased to 900℃ at a rate of 10℃ / min and held for 1 hour, then allowed to cool naturally to room temperature. After grinding evenly, the sample was ready for use. The sample obtained in this stage was labeled PANI. DBSA / MA 0.5 -Fe(SC) -HT2.

[0100] Example 8

[0101] A self-supported Fe-NC oxygen reduction catalyst was prepared by the following method:

[0102] 1) Take 0.4g NaCl and 2mL aniline and add them to 0.5M HCl solution. After ultrasonic dispersion (~1h), keep below 10℃ and add a certain amount of 1M ammonium persulfate dropwise while stirring continuously. After about 0.5h, add 5mL of FeCl3·6H2O aqueous solution dropwise and continue stirring for 24h to allow aniline to be fully oxidized and polymerized into PANI. Then, filter, evaporate and dry the above mixture in sequence.

[0103] 2) Add 0.5g of urea (UR) to the above mixture, mix in the solid phase, and grind evenly.

[0104] 3) Spread the above solid powder evenly in a quartz boat and place it in a tube furnace, heating at 200 mL / min. -1 Under N2 purging, the temperature is increased to 900℃ at 10℃ / min and maintained for 1 hour, then allowed to cool naturally to room temperature. The material is then ground uniformly. The product at this stage is named PANI / UA. 0.5 -Fe (SC) -HT1.

[0105] 4) Add PANI / UA 0.5 -Fe (SC) -HT1 was added to 30 mL of 0.5 M H2SO4 solution at 60 °C for acid treatment for 8 hours. After treatment, the solution was filtered, washed, and dried. The product at this stage was named PANI / UA. 0.5 -Fe (SC) -AL.

[0106] 5) Take 0.15g PANI / UA 0.5 -Fe (SC) -AL at 200mL min -1 Under N2 protection, the temperature was increased to 900℃ at a rate of 10℃ / min and held for 1 hour, then allowed to cool naturally to room temperature. After grinding evenly, the sample was ready for use. The sample obtained in this stage was labeled as PANI / UA. 0.5 -Fe (SC) -HT2.

[0107] Example 9

[0108] A self-supported Fe-NC oxygen reduction catalyst was prepared by the following method:

[0109] 1) Take 0.4g NaCl and 2.1mL pyrrole and add them to 0.5M HCl solution. After ultrasonic dispersion (~1h), keep below 10℃ and add a certain amount of 1M ammonium persulfate dropwise while stirring continuously. After about 0.5h, add 5mL of FeCl3·6H2O aqueous solution dropwise and continue stirring for 24h to allow aniline to be fully oxidized and polymerized into PANI. Then, filter, evaporate and dry the above mixture in sequence.

[0110] 2) Add 0.5g of melamine (MA) to the above mixture, mix in the solid phase, and grind evenly.

[0111] 3) Spread the above solid powder evenly in a quartz boat and place it in a tube furnace, heating at 200 mL / min. -1 Under N2 purging, the temperature is increased to 900℃ at 10℃ / min and maintained for 1 hour, then allowed to cool naturally to room temperature. The material is then ground until homogeneous. The product at this stage is named PPY / MA. 0.5 -Fe (SC) -HT1.

[0112] 4) PPY / MA 0.5 -Fe (SC) -HT1 was added to a 30 mL 0.5 M H2SO4 solution at 60 °C for acid treatment for 8 hours. After treatment, the solution was filtered, washed, and dried. The product at this stage was named PPY / MA. 0.5 -Fe (SC) -AL.

[0113] 5) Take 0.15g PPY / MA 0.5 -Fe (SC) -AL at 200mL min -1 Under N2 protection, the temperature was increased to 900℃ at a rate of 10℃ / min and held for 1 hour, then allowed to cool naturally to room temperature. After grinding evenly, the sample was ready for use. The sample obtained in this stage was labeled PPY / MA. 0.5 -Fe (SC) -HT2.

[0114] Working electrode fabrication and ORR performance testing:

[0115] Weigh 3 mg of the self-supported Fe-NC catalyst prepared in Examples 1, 2, and 3, disperse it in a 0.5 mL mixed solution of 5 wt% Nafion and deionized water (1 / 9, V / V), and sonicate for 1 h. Then, transfer 15 μL of the uniformly dispersed catalyst suspension to the polished glassy carbon electrode surface, bake it under an infrared lamp, and use it as the working electrode after the solvent has completely evaporated and dried. Then, use a platinum wire and an Ag / AgCl electrode as the counter electrode and reference electrode, respectively, and test the ORR activity of the material in 0.1 M KOH by cyclic voltammetry (CV) and linear sweep voltammetry (LSV).

[0116] PANI / MA synthesized in Examples 1, 2, and 3 0.5 -Fe-HT2, PANI-Fe (SC) -HT2 and PANI / MA 0.5 -Fe (SC) The polarization curves and activity parameters of the electrocatalytic ORR of -HT2 in 0.1M KOH at 1600 rpm are as follows: Figure 6 As shown in Table 2; PANI / MA 0.5 -Fe (SC) The polarization curves of ORR catalyzed by -HT2 at different rotational speeds and the number of electrons transferred per O2 molecule at different potentials are as follows: Figure 7 As shown.

[0117] PANI / MA synthesized in Example 3 0.5 -Fe (SC) The methanol resistance test of -HT2 was conducted as follows: with the potential constant at 0.57V vs. RHE and the electrode rotation speed at 1600rpm, the test was first conducted in 0.1M KOH saturated with N2 for 5 minutes, then switched to O2 and continued for a period of time. At this time, a certain amount of methanol was quickly added, and the test was continued for a period of time. The methanol resistance test at a higher potential was conducted in the same manner as above, except that the potential was kept constant at 0.85V.

[0118] PANI / MA synthesized in Example 3 0.5 -Fe (SC) The methanol resistance properties of -HT2 and commercial Pt / C at 0.57V and 0.85V are as follows: Figure 8 , 9 As shown.

[0119] PANI / MA synthesized in Example 3 0.5 -Fe (SC)The stability of -HT2 was tested as follows: After measuring the polarization curve of the sample at 1600 rpm in an oxygen-saturated 0.1 MkOH solution, the polarization curve was retested after 15,000 cyclic voltammetry scans within a potential range of 0.6–1.05 V vs. RHE at a scan rate of 50 mV / s. The half-wave potentials read from the polarization curves before and after the two cycles were then compared.

[0120] PANI / MA synthesized in Example 3 0.5 -Fe (SC) -HT2-catalyzed ORR stability as Figure 10 As shown.

[0121] In the embodiments of this invention, the commercial Pt / C (20 wt.% Pt) used for comparison was manufactured by Johnson Matthey. Unless otherwise specified, the characterization and electrochemical testing methods used in the embodiments are conventional techniques in the art.

[0122] Table 1 Structural property parameters of self-supported Fe-NC oxygen reduction catalyst

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[0124] Table 2. Activity parameters of the self-supported Fe-NC catalyst for ORR in 0.1 M KOH.

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[0126]

[0127] As can be seen from Tables 1 and 2, the self-supported Fe-NC catalyst (PANI / MA) synthesized in Example 3 was applied. 0.5 -Fe (SC) -HT2) has a large mesopore size (~9.7 nm) and a very high specific surface area (1124 m²). 2 g -1 Its catalytic ORR has very high onset and half-wave potentials, which are 10 mV and 40 mV higher than those of commercial Pt / C catalysts (JM, 20 wt% Pt), respectively. The kinetic current density at high potentials is even 4 times that of Pt / C.

[0128] Polarization curves and initial potentials (E) obtained for ORR catalyzed by a series of self-supported Fe-NC catalysts and Pt / C catalysts prepared in Examples 1, 2, and 3. onset ), half-wave potential (E) 1 / 2 ), limiting current density (J L ) and dynamic current density (J k )like Figure 6As shown in Table 2; ORR at different rotational speeds in PANI / MA prepared in Example 3 0.5 -Fe (SC) The polarization curves on -HT2 and the corresponding KL equation fitting lines at different potentials (built-in graphs) are as follows: Figure 7 As shown.

[0129] Figure 1 , 2 TEM images, HAADF and elemental mapping images, and XRD spectra of Example 3 are shown, indicating that the self-supported Fe-NC oxygen reduction catalyst exhibits an irregular particle and plate-like aggregate morphology, and the iron species it contains are highly dispersed with almost no crystalline iron species particles. Figure 3 , 4 The Raman spectrum and XPS full spectrum of Example 3 are shown, demonstrating that the self-supported Fe-NC oxygen reduction catalyst has a high degree of carbon defects, and its surface mainly contains C, N, O and Fe elements, with a low Fe content. Figure 5 The N2 adsorption / desorption isotherms and pore size distribution of Example 3 are shown. Combined with the texture parameters in Table 1, it is shown that the average pore size of the BJH desorption of the self-supported Fe-NC oxygen reduction catalyst is 9.7 nm, the most probable pore size is 2.1 nm, and the pore volume is 0.50 cm³. 3 g -1 And its specific surface area is as high as 1124 m² 2 g -1 The above results demonstrate that by utilizing the multiple effects of nitrogen-doped additives and inorganic salt activators, specific structural properties such as highly dispersed iron species, a high degree of carbon defects and graphitization, abundant hierarchical pore structure, large mesopore size, and high specific surface area can be tailored simply by pyrolyzing nitrogen-containing precursors.

[0130] Figure 6 Table 2 shows the electrochemical performance of the three samples synthesized in Examples 1, 2, and 3 and the Pt / C catalyst in O2-saturated 0.1 MkOH for ORR catalysis. The results show that the PANI / MA synthesized in Example 3... 0.5 -Fe (SC) -HT2 exhibits the highest catalytic performance for ORR, with its E onset E 1 / 2 J L and J k (0.87V) respectively up to 1.0V, 0.90V, and 4.85mA cm -2 and 12.2mAcm -2These parameters are even higher than those of Pt / C. Comparing the catalytic activity of the three samples synthesized in Examples 1, 2 and 3 for ORR, it is shown that only by simultaneously introducing melamine (MA) and the inorganic salt NaCl can a self-supported Fe-NC catalyst with high activity for ORR be constructed. Figure 7 , 8 Figures 9 and 9 respectively show the PANI / MA synthesized in Example 3. 0.5 -Fe (SC) The results show that HT2 catalyzes ORR via a 4-electron reaction pathway and exhibits better methanol resistance than Pt / C at both relatively low and high potentials. Figure 10 The PANI / MA synthesized in Example 3 is shown. 0.5 -Fe (SC) The polarization curves of the ORR catalyzed by HT2 after the first test and after passing the accelerated stability test (15,000 cycles) showed a difference of only 0.9 mV in half-wave potential, which is almost negligible, demonstrating good operational stability.

[0131] The above results reveal a self-supported Fe-NC oxygen reduction catalyst (PANI / MA) derived using polyaniline (PANI) as a nitrogen-containing precursor and melamine (MA) as a nitrogen-doping agent, respectively, and through the interaction of inorganic salts. 0.5 -Fe (SC) -HT2) possesses high nitrogen doping content, highly dispersed iron species, a high degree of carbon defects and graphitization, abundant hierarchical pore structure, large mesopore size, and high specific surface area. These characteristics are highly beneficial for increasing active site density, improving active site utilization, mass transfer and diffusion of substrate products, and rapid electron transfer, thereby synergistically resulting in excellent ORR performance; In addition, Example 3 synthesizes PANI / MA 0.5 -Fe (SC) The method described in -HT2 features low raw material cost, low reagent toxicity, safe and environmentally friendly process, simple and controllable method, large space for process optimization, and high material productivity. Under optimized preparation conditions, it has great potential to synergistically produce self-supported Fe-NC materials with even better ORR performance. The above embodiments are merely specific embodiments of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention, and these obvious substitutions all fall within the protection scope of the present invention.

Claims

1. An inorganic salt-assisted derived self-supported Fe-NC oxygen reduction electrocatalyst, characterized in that: The self-supported Fe-NC oxygen reduction catalyst is an irregular particle and / or sheet-like aggregate; The carbon content is 82.64-90.64 at.%, the nitrogen content is 2.95-5.95 at.%, and the fe content is 0.06-0.28 at.%. The average mesopore size is 9.7 ± 0.2 nm, the most probable pore size is 2.1 nm, and the specific surface area is 1124 ± 5 ​​m². 2 g -1 ; The self-supported Fe-NC oxygen reduction catalyst includes a nitrogen-containing precursor, a nitrogen-doped pore-forming agent, and a nitrogen-containing precursor molecular structure regulator. The nitrogen-containing precursor is polyaniline, the nitrogen-doped pore-forming agent is melamine, and the inorganic salt is one or a combination of two or more of AlCl3, NaF, NaCl, NaBr, NaI, KCl, MgCl2, and / or NH4Cl. The nitrogen-containing precursor molecular structure regulator includes an inorganic salt, and the mass ratio of the nitrogen-containing precursor to the nitrogen-doped pore-forming agent is 2:1 to 20. The preparation method of this self-supported Fe-NC oxygen reduction electrocatalyst includes the following steps: S1. Preparation of solid powder A: First, an inorganic salt, which serves as a molecular structure regulator for nitrogen-containing precursors, is added to an acidic aqueous solution. Then, the monomer of the nitrogen-containing precursor is added and ultrasonically dispersed evenly. Next, an aqueous solution of ammonium persulfate and FeCl3·6H2O is added dropwise and stirred continuously. Finally, the mixed solution is filtered, dried, and ground to obtain solid powder A. S2. Preparation of catalyst precursor: A obtained in step S1 is mixed with melamine, which is used as a nitrogen doping agent and pore-forming agent, in a solid phase to obtain the catalyst precursor. S3. Preparation of primary catalyst: The B obtained in step S2 is heated to 850-950℃ at 10±5℃ / min and held for 1-3 h under the protection of flowing inert gas. Then it is naturally cooled to room temperature and ground uniformly to obtain the primary catalyst. S4. Acid treatment of the catalyst: The primary catalyst obtained in step 3) is impregnated in an acid solution of 0.5-2 M at 60-80℃ and stirred for 0.5-24 h. After the treatment, it is filtered, washed and dried to obtain a self-supported Fe-NC catalyst with some iron species removed. S5. Secondary heat treatment of the catalyst: The self-supported Fe-NC catalyst obtained in step S4 is subjected to heat treatment at 180–220 mL / min. -1 Under the protection of flowing gas, the temperature is increased to 800-1000℃ at 10±5℃ / min and held for 0.5-3 h, and then naturally cooled to room temperature to obtain the final self-supported Fe-NC oxygen reduction catalyst.

2. The inorganic salt-assisted derived self-supported Fe-NC oxygen reduction electrocatalyst according to claim 1, characterized in that: In step S2, solid-phase mixing is solid-phase grinding and / or ball milling mixing.

3. The inorganic salt-assisted derived self-supported Fe-NC oxygen reduction electrocatalyst according to claim 1, characterized in that: In step S3, the flowing inert gas is nitrogen and / or argon.

4. The inorganic salt-assisted derived self-supported Fe-NC oxygen reduction electrocatalyst according to claim 1, characterized in that: In step S5, the flowing gas is nitrogen and / or argon.

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