CN112397734B - Preparation method and application of a high-density Fe-N4 active site oxygen reduction electrocatalyst - Google Patents

Abstract

The invention provides high-density Fe-N₄Preparation method of active site oxygen reduction electrocatalyst and active site oxygen reduction electrocatalystThe application belongs to the field of polymer electrolyte membrane fuel cell catalysts. Uniformly dispersing metal zirconium salt in a solvent, wherein Zr in the zirconium salt⁴⁺Adding two macrocyclic compounds including macrocyclic compound I, metal macrocyclic compound II and organic acid into solvent at concentration of 2-8mg/ml, ultrasonic treating at 20-40 deg.C for 10-30min, reacting at 120 deg.C for 8-12h, vacuum filtering, washing until the filtrate is colorless, oven drying, and pyrolyzing at 600-900 deg.C for 1-2h to obtain high-density Fe-N₄An active site oxygen reduction electrocatalyst. The method is simple to operate, easy to control and environment-friendly, and the prepared high-density Fe-N is₄The active site oxygen reduction electrocatalyst has excellent oxygen reduction activity and can be used for polymer electrolyte membrane fuel cells.

Description

Preparation method and application of a high-density Fe-N4 active site oxygen reduction electrocatalyst

technical field

The invention relates to the field of a polymer electrolyte membrane fuel cell cathode oxygen reduction electrocatalyst, in particular to a preparation method and application of a high-density Fe- _N4 active site oxygen reduction electrocatalyst.

Background technique

Since the development of modern industrialization, the massive and unreasonable use of non-renewable fossil fuels such as coal, oil, and natural gas has led to a sharp increase in the global emissions of harmful gases such as nitrogen, sulfur, and carbon (NO _x , SO _x , CO ), causing It addresses a series of global concerns such as global temperature rise, environmental degradation, human health and the global energy crisis. Therefore, it is urgent to develop environmentally friendly, sustainable, safe and efficient energy technologies. Polymer electrolyte membrane fuel cells (PEMFCs) have attracted worldwide attention due to their high energy conversion efficiency, environmental friendliness, rapid start-up at room temperature, no electrolyte loss, and high specific power and specific energy.

Electrocatalysts with high activity and high stability are one of the important constituent materials of PEMFCs. The emergence of platinum (Pt)-based catalysts has greatly promoted the development of fuel cells and advanced the practical application of fuel cells. However, the low global reserves of Pt lead to its relatively high price. In addition, Pt-based electrocatalysts suffer from poor stability (prone to dissolution and re-aggregation) and poor tolerance to reactive species (e.g., methanol) in the actual working conditions of fuel cells, These problems make electrocatalysts one of the key factors hindering the commercialization of fuel cells. Faced with the above problems, scientists propose two strategies. The first strategy is to develop Pt-M ₁ (M ₁ can be noble metals such as Pd, Au, or transition metals such as Fe, Co, and Ni) materials, which can be controlled by morphology. , develop alloys, reduce the amount of Pt, and improve the catalytic activity and durability of electrocatalysts; the second strategy: develop non-noble metal oxygen reduction electrocatalysts, in this type of electrocatalysis, M ₂ -NC (M ₂ is mainly Fe , Co, Mn and other transition metals) non-precious metal electrocatalysts have received extensive attention due to their low cost, high activity, high durability, and methanol resistance.

In the 1960s, Jasinski first reported the oxygen reduction activity of N ₄ -chelate cobalt phthalocyanine in alkaline electrolytes, which opened a new field of research on non-noble metal oxygen reduction electrocatalysts. (Nature, 1964, 201, 1212-1213) Since then, many M ₂ -NC non-noble metal oxygen reduction electrocatalysts based on metallophthalocyanine and metalloporphyrin macrocyclic compounds have been widely reported. For example, Wei's team obtained an electrocatalyst with high oxygen reduction activity and good durability by loading iron porphyrin on carbon materials by covalent bond (Angew.Chem., 2014, 126, 6777-6781 ). Metal macrocycles are good precursors for non-noble metal oxygen reduction electrocatalysts due to their unique M2 _{- N4} structure. Currently, oxygen reduction electrocatalysts based on metallophthalocyanine or metalloporphyrin-based macrocycles The preparation principle is mainly to complete the intermolecular stacking through many forces (such as: π-π interaction, positive and negative charge interaction, hydrogen bonding), and then high temperature pyrolysis carbonization in an inert atmosphere to improve the stability of the material, however, thermal Uncontrollability in the solution process can often lead to metal aggregation, resulting in reduced material utilization. Therefore, there is an urgent need for a strategy to improve the utilization of metal macrocycles in the preparation of oxygen reduction electrocatalysts. The emergence of metal-organic frameworks (MOFs) realizes metal phthalocyanine or metalloporphyrin-like macrocycles from disordered molecular stacking into an ordered molecular arrangement.

MOFs are organic-inorganic hybrid materials formed by organic ligands and metal ions or polynuclear metal clusters through coordination bonds. Due to the strong oriented coordination bonds, they are well defined in geometry and crystallography. Topology. MOFs have the characteristics of porosity, easy functionalization, good designability, and high specific surface area. The two important constituent units of MOFs—metal ions or clusters and organic ligands—provide a variety of possibilities for the synthesis of such materials. With the in-depth research on synthesis and structural characterization, more and more MOFs materials have been discovered and applied in optics, magnetism, and electricity, as well as in catalysis, gas storage, and separation.

MOFs materials have developed rapidly. In 2008, Xu's team first reported the use of MOF-5 as a precursor to prepare porous carbon supports after high temperature pyrolysis and applied in the field of oxygen reduction (JOURNAL OF THE AMERICAN CHEMICALSOCIETY, 2008, 130(16): 5390-5391.). The structure of MOFs is stable. After high _- temperature pyrolysis carbonization, its electrical conductivity can be greatly improved and its porous properties can be retained, which is beneficial to the transport of O _{2 .} Species attack on the active sites of catalysts, extending the lifetime of electrocatalysis.

With the development of MOFs materials, scientists have realized the use of macrocyclic compounds as organic ligands of MOFs, and synthesized a series of zirconium-based metal cluster MOFs (Angew.Chem.Int.Ed.2012,51, 10307-10310), and Gradually applied in the field of electrocatalysis. For example, in 2017, Jiang Hailong's team synthesized PCN-224MOFs materials using Zr ₆ clusters as metal clusters and m-tetrakis(4-carboxyphenyl) porphine (TCPP) as ligands. Adsorption, high-temperature pyrolysis, and acid wash etching resulted in structurally stable catalysts whose durability was greatly improved (ChemSusChem, 2017, 10, 1-7). By combining with the structure of MOFs, although the activity and durability of metal macrocyclic compounds are greatly improved, the catalytic activity of electrocatalysts prepared by this method still cannot meet the activity requirements of PEMFCs, and it is difficult to be applied to proton exchange membrane fuel cells. Therefore, a strategy to increase the active site density of electrocatalysts to enhance their catalytic activity is urgently needed to accelerate the development of PEMFCs.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a preparation method and application of a high-density Fe- _N4 active site oxygen reduction electrocatalyst, which is simple to operate, easy to control, and environmentally friendly. The described high-density Fe- _N4 active site oxygen reduction electrocatalyst uses two macrocyclic compounds as raw materials, among which one macrocyclic compound I (named _Zr6 -Porphyrin) is ionically coordinated with _Zr6 metal clusters. Bonded in the form of bonds to form a three-dimensional porous highly crystalline material with a high specific surface area and two pore sizes of micropores (<2nm) and mesopores (2-50nm), and another with oxygen reduction before the three-dimensional structure of MOFs was formed. The catalytically capable metal macrocyclic compound II (named Precursor-porphyrin) binds to Zr ₆ metal clusters through ionic coordination bonds, and simultaneously inserts Precursor-porphyrin into the mesopores of MOFs while synthesizing MOFs. The active site is then prepared by high-temperature pyrolysis carbonization to obtain a high-density Fe- _N4 active site oxygen reduction electrocatalyst with excellent oxygen reduction comprehensive performance, which is suitable for proton exchange membrane fuel cells.

In order to achieve the above object, the technical scheme of the present invention is:

A preparation method of a high-density Fe-N ₄ active site oxygen reduction electrocatalyst, comprising the following steps:

The metal salt of zirconium (zirconium salt) is uniformly dispersed in the solvent, wherein the concentration of Zr ⁴⁺ in the solvent in the zirconium salt is 2-8 mg/ml, and two macrocyclic compounds including macrocyclic compound I (named Zr ₆ -Porphyrin), metal macrocyclic compound II (named Precursor-Porphyrin)) and organic acid, at 20-40 ℃, ultrasonic treatment for 10-30min, react at 120 ℃ for 8-12h, suction filtration, wash until The filtrate is colorless, dried, and pyrolyzed at 600-900 °C for 1-2 h to obtain a high-density Fe-N ₄ active site oxygen reduction electrocatalyst;

The mass ratio of the macrocyclic compound I (Zr ₆ -Porphyrin) to the zirconium salt is (0.1-0.4):1, preferably 0.37:1;

The mass ratio of the metal macrocyclic compound II (Precursor-Porphyrin) to the macrocyclic compound I (Zr ₆ -Porphyrin) is (0.25-1):1;

The material ratio of described organic acid and zirconium salt is (20-30): 1;

Based on the above technical solutions, preferably, the zirconium salt includes one or more of ZrCl ₄ , ZrOCl ₂ ·8H ₂ O, and ZrO(NO ₃ ) ₂ ·H ₂ O.

Based on the above technical solutions, preferably, the organic acid includes CH ₂ O ₂ , C ₂ H ₄ O ₂ , C ₂ HF ₃ O ₂ , C ₃ H ₆ O ₂ , C ₄ H ₈ O ₂ , C ₂ H One or a mixture of two or more of ₂ Cl ₂ O ₂ , C ₇ H ₆ O ₂ and C ₈ H ₈ O ₂ .

Based on the above technical solutions, preferably, the macrocyclic compound I (Zr ₆ -Porphyrin) is a porphyrin or phthalocyanine with four carboxyl groups in the side chain, wherein the center of the macrocyclic compound is free of metal elements and/or Including metal elements, if metal porphyrin or phthalocyanine is involved, the metal is iron; the metal macrocyclic compound II (Precursor-porphyrin) is Heme.

Based on the above technical solutions, preferably, the solvent includes ethanol, propanol, isopropanol, dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), N,N-dimethylformamide One or a mixture of two or more of acetamide (DMAC).

Based on the above technical solutions, preferably, the rate of heating up to the pyrolysis temperature is 1-10°C/min.

The present invention also relates to protecting the high-density Fe-N ₄ active site oxygen reduction electrocatalyst obtained by the above preparation method.

The present invention also relates to the application of protecting the above-mentioned high-density Fe- _N4 active site oxygen reduction electrocatalyst in a proton exchange membrane fuel cell.

The invention proposes a preparation method of a high-density Fe- _N4 active site oxygen reduction electrocatalyst, which uses two macrocyclic compounds as raw materials, wherein one macrocyclic compound (named as Zr ₆ -Porphyrin) and Zr ₆ metal group Clusters are combined in the form of ionic coordination bonds to grow into MOFs with three-dimensional spatial structure, and another metal macrocyclic compound (named Precursor-porphyrin) is used as a precursor to increase the density of active sites without affecting mass transfer. Precursor-porphyrin was embedded into the pores of MOFs materials to improve the active site density of oxygen reduction electrocatalysts. The high density Fe- _N4 active site oxygen reduction electrocatalysts prepared by this method exhibited excellent oxygen reduction catalytic activity. and stability.

Compared with the prior art, the outstanding features of the present invention are: 1) The metal macrocyclic compound with catalytic activity is embedded in the mesopores of the MOFs material generated by using another macrocyclic compound as an organic ligand, which improves the electrical conductivity. The active site density of the catalyst; 2) MOFs are porous, and their mesoporous structure is not completely filled by metal macrocyclic compounds, which is still conducive to O transport; ₃ ) After the MOFs are pyrolyzed, their electrical conductivity is improved, and at the same time , its three-dimensional structure will also be partially retained, which is helpful to improve the catalytic activity of oxygen reduction; 4) the utilization of MOFs structure may be beneficial to the four-electron oxygen reduction process, reducing the generation of H ₂ O ₂ that can attack the porphyrin ring, Extend the life of electrocatalysts. 5) The present invention is simple to operate, easy to control, and environmentally friendly, and the prepared high-density Fe-N ₄ active site oxygen reduction electrocatalyst has excellent oxygen reduction activity, which can be used in polymer electrolyte membrane fuel cells.

Description of drawings

1 is a SEM image of the electrocatalyst precursor obtained in the present invention, wherein a is the electrocatalyst precursor PCN-222 obtained in Comparative Example 1; b is the electrocatalyst precursor 20-Heme@Fe ₁₀ -PCN-222 obtained in Example 1;

Figure 2 is an XRD comparison diagram of the electrocatalyst precursor PCN-222 obtained in Comparative Example 1, the electrocatalyst precursor 20-Heme@Fe ₁₀ -PCN-222 obtained in Example 1, and the simulated PCN-222;

Figure 3 is the electrocatalyst precursor PCN-222 obtained in Comparative Example 1, the electrocatalyst precursor 20-Heme@PCN-222 obtained in Example 3, and the electrocatalyst precursor 20-Heme@Fe ₁₀ -PCN-222 obtained in Example 1. Pore size distribution map;

Figure 4 shows the ORR polarization of the product PCN-222-700 obtained in Comparative Example 1, the product 20-Heme@PCN-222-700 obtained in Example 3 and the product 20-Heme@Fe ₁₀ -PCN-222-700 obtained in Example 1 Graph.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and examples. The following examples are only to illustrate the present invention more clearly, but the claimed scope of the present invention is not limited to the scope expressed by the following examples.

Example 1

Disperse 40 mg of ZrOCl ₂ ·8H ₂ O in 8 mL of DMF solution, add 650 mg of benzoic acid, 20 mg of Heme, 30 mg of meso-tetrakis(4-carboxyphenyl) porphine (TCPP), and 10 mg of meso-tetrakis(4-carboxyphenyl) Porphine ferric chloride (Fe-TCPP), sonicated for 30 min at 25 °C, reacted at 120 °C for 12 h, suction filtered, washed until the filtrate was colorless, and dried at 65 °C to obtain the precursor of the electrocatalyst, denoted as 20 -Heme@Fe ₁₀ -PCN-222, then the precursor was heated at a rate of 5 °C/min to 700 °C and then held at a constant temperature for 2 h, and finally a black powder solid was obtained, denoted as 20-Heme@Fe ₁₀ -PCN-222-700.

As shown in Figure 1, the prepared electrocatalyst precursor 20-Heme@Fe ₁₀ -PCN-222 obtained in Example 1 is rod-shaped and uniform in size, and is consistent with the initial PCN-222 morphology of the electrocatalyst precursor obtained in Example 2 , but its size is reduced.

As shown in Figure 2, the XRD diffraction peaks of the precursors of the prepared electrocatalysts are consistent with the peak positions of the simulated MOFs, indicating that the introduction of Heme does not have the structure of MOFs, and the obtained precursors are highly crystalline materials.

As shown in Figure 3, the prepared electrocatalyst precursor 20-Heme@Fe ₁₀ -PCN-222 obtained in Example 1, the initial PCN-222 electrocatalyst precursor obtained in Example 2 and the electrocatalyst precursor 20- It can be seen from the pore size distribution of Heme@PCN-222 that the prepared precursors contain both micropores and mesopores. In addition, when Heme is introduced, the obtained precursor 20-Heme@Fe ₁₀ -PCN-222 The mesopore volume of 20-Heme@PCN-222 is reduced, which directly proves that Heme is embedded in the mesopores of MOFs.

As shown in Figure ₄ , the electrochemical performance of the oxygen reduction reaction was measured by the standard three-electrode method. The catalyst was made into a thin-film working electrode. Potential sweep tests were performed at a voltage of 0-1.2V (vsRHE), and the electrode speed was 1600 r/min. The polarization curves show that with the introduction of Heme and Fe-TCPP, the activity of the electrocatalyst gradually increases, indicating that the introduction of Heme and Fe-TCPP gradually increases the active site density of the electrocatalyst and improves the catalytic activity of the electrocatalyst.

Comparative Example 1

Disperse 40 mg of ZrOCl ₂ ·8H ₂ O in 8 mL of DMF solution, add 650 mg of benzoic acid and 40 mg of TCPP, sonicate for 30 min at 25 °C, react at 120 °C for 12 h, filter with suction, wash until the filtrate is colorless, at 65 °C After drying, the precursor of the electrocatalyst was obtained, denoted as PCN-222, and then the precursor was heated at a rate of 5 °C/min to 700 °C and kept at a constant temperature for 2 h to finally obtain a black powder solid, denoted as PCN-222-700.

Example 2

Disperse 40 mg of ZrOCl ₂ ·8H ₂ O in 8 mL of DMF solution, add 650 mg of benzoic acid, 10 mg of Heme, 40 mg of TCPP, sonicate for 30 min at 25 °C, react at 120 °C for 12 h, suction filtration, and wash until the filtrate is colorless, at 65 °C The precursor of the electrocatalyst was obtained by drying under low temperature, which was denoted as 10-Heme@PCN-222. After that, the precursor was heated at a rate of 5 °C/min to 700 °C and then kept at a constant temperature for 2 h, and finally a black powder solid was obtained, which was denoted as 10-Heme. @PCN-222-700.

Example 3

Disperse 40 mg of ZrOCl ₂ ·8H ₂ O in 8 mL of DMF solution, add 650 mg of benzoic acid, 20 mg of Heme, 40 mg of TCPP, sonicate for 30 min at 25 °C, react at 120 °C for 12 h, filter with suction, and wash until the filtrate is colorless, at 65 °C The precursor of the electrocatalyst was obtained by drying under low temperature, which was denoted as 20-Heme@PCN-222. Then the precursor was heated at a rate of 5 °C/min to 700 °C and kept at a constant temperature for 2 h, and finally a black powder solid was obtained, which was denoted as 20-Heme. @PCN-222-700.

Example 4

Disperse 40 mg of ZrOCl ₂ ·8H ₂ O in 8 mL of DMF solution, add 650 mg of benzoic acid, 30 mg of Heme, 40 mg of TCPP, sonicate for 30 min at 25 °C, react at 120 °C for 12 h, suction filtration, and wash until the filtrate is colorless, at 65 °C drying under low temperature to obtain the precursor of the electrocatalyst, denoted as 30-Heme@PCN-222, then the precursor was heated at a rate of 5 °C/min to 700 °C and kept at a constant temperature for 2 h, finally a black powder solid was obtained, denoted as 30-Heme @PCN-222-700.

Example 5

Disperse 40 mg of ZrOCl ₂ ·8H ₂ O in 8 mL of DMF solution, add 650 mg of benzoic acid, 40 mg of Heme, 40 mg of TCPP, sonicate for 30 min at 25 °C, react at 120 °C for 12 h, filter with suction, and wash until the filtrate is colorless, at 65 °C drying under low temperature to obtain the precursor of the electrocatalyst, denoted as 40-Heme@PCN-222, then the precursor was heated at a rate of 5 °C/min to 700 °C and kept at a constant temperature for 2 h, finally a black powder solid was obtained, denoted as 40-Heme @PCN-222-700.

Example 6

Disperse 40 mg of ZrOCl ₂ ·8H ₂ O in 8 mL of DMF solution, add 650 mg of benzoic acid, 20 mg of Heme, 35 TCPP, 5 mg of Fe-TCPP, sonicate for 30 min at 25 °C, react at 120 °C for 12 h, suction filtration, and wash until the filtrate is Colorless, dried at 65°C to obtain the precursor of the electrocatalyst, denoted as 20-Heme@Fe ₅ -PCN-222, and then the precursor was heated at a rate of 5°C/min to 700°C and kept at a constant temperature for 2h, and finally obtained Black powder solid, denoted as 20-Heme@Fe ₅ -PCN-222-700.

Example 7

Disperse 40 mg of ZrOCl ₂ ·8H ₂ O in 8 mL of DMF solution, add 650 mg of benzoic acid, 20 mg of Heme, 20 TCPP, 20 mg of Fe-TCPP, ultrasonicate for 30 min at 25 °C, react at 120 °C for 12 h, suction filtration, and wash until the filtrate is free of After drying at 65 °C, the precursor of the electrocatalyst was obtained, which was denoted as 20-Heme@Fe ₂₀ -PCN-222. Then the precursor was heated at a rate of 5 °C/min to 700 °C and kept at a constant temperature for 2 h, and finally a black color was obtained. Powder solid, denoted 20-Heme@Fe ₂₀ -PCN-222-700.

Example 8

Disperse 40 mg of ZrOCl ₂ ·8H ₂ O in 8 mL of DMF solution, add 650 mg of benzoic acid, 20 mg of Heme, 10 TCPP, 30 mg of Fe-TCPP, sonicate for 30 min at 25 °C, react at 120 °C for 12 h, suction filtration, and wash until the filtrate is free of After drying at 65 °C, the precursor of the electrocatalyst was obtained, which was denoted as 20-Heme@Fe ₃₀ -PCN-222. Then the precursor was heated at a rate of 5 °C/min to 700 °C and kept at a constant temperature for 2 h, and finally a black color was obtained. Powder solid, denoted 20-Heme@ _Fe30 -PCN-222-700.

Example 9

Disperse 40 mg of ZrOCl ₂ ·8H ₂ O in 8 mL of DMF solution, add 650 mg of benzoic acid, 20 mg of Heme, 40 mg of Fe-TCPP, sonicate for 30 min at 25 °C, react at 120 °C for 12 h, filter with suction, wash until the filtrate is colorless, Drying at 65 °C to obtain the precursor of the electrocatalyst, denoted as 20-Heme@Fe ₄₀ -PCN-222, then the precursor was heated at a rate of 5 °C/min to 700 °C and then kept at a constant temperature for 2 h, and finally a black powder solid was obtained. , denoted 20-Heme@Fe ₄₀ -PCN-222-700.

Claims (6)

1. a high-density Fe-N ₄ preparation method of active site oxygen reduction electrocatalyst, is characterized in that, comprises the following steps: Disperse the zirconium salt evenly in the solvent, add the macrocyclic compound I, the metal macrocyclic compound II and the organic acid, at 20-40 °C, ultrasonically treat for 10-30 min, react at 120 °C for 8-12 h, suction filtration, Wash until the filtrate is colorless, dry, and pyrolyze at 600-900 °C for 1-2 h to obtain a high-density Fe-N ₄ active site oxygen reduction electrocatalyst; The substance ratio of the macrocyclic compound I and the zirconium salt is 0.1-0.4:1; The mass ratio of the metal macrocyclic compound II to the macrocyclic compound I is 0.25-1:1; The material ratio of described organic acid and zirconium salt is 20-30:1; The macrocyclic compound I is a porphyrin or phthalocyanine or porphine containing four carboxyl groups in the side chain, wherein the center of the macrocyclic compound I is free of metal elements and/or includes metal elements, and the metal is iron ; the metal macrocyclic compound II is hematoxylin; The zirconium salt is one or more of ZrCl ₄ , ZrOCl ₂ ·8H ₂ O, and ZrO(NO ₃ ) ₂ ·H ₂ O; The organic acids are CH ₂ O ₂ , C ₂ H ₄ O ₂ , C ₂ HF ₃ O ₂ , C ₃ H ₆ O ₂ , C ₄ H ₈ O ₂ , C ₂ H ₂ Cl ₂ O ₂ , C ₇ One or a mixture of two or more of H ₆ O ₂ and C ₈ H ₈ O ₂ . 2. the preparation method of a kind of high-density Fe _- N active site oxygen reduction electrocatalyst according to claim 1, is characterized in that, described solvent is ethanol, propanol, isopropanol, dimethyl methylene One or more mixtures of sulfone, N,N-dimethylformamide and N,N-dimethylacetamide. 3. the preparation method of a kind of high-density Fe _- N active site oxygen reduction electrocatalyst according to claim 1, is characterized in that, the concentration of the zirconium in described zirconium salt in solvent is 2-8mg/ ml. 4 . The preparation method of a high-density Fe-N ₄ active site oxygen reduction electrocatalyst according to claim 1 , wherein the rate of heating up to the pyrolysis temperature is 1-10° C./min. 5 . 5. The high-density Fe-N ₄ active site oxygen reduction electrocatalyst prepared by the preparation method of any one of claims 1-4. 6. Application of the high-density Fe- _N4 active site oxygen reduction electrocatalyst of claim 5 in fuel cells.

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