Electrocatalytic oxygen reduction material as well as preparation and application thereof

Abstract

The invention discloses an electrocatalytic oxygen reduction material as well as preparation and application thereof. According to the invention, by introducing a synergistic effect between Fe clusters and Fe-Co diatomic sites, the oxygen reduction reaction activity in the acidic electrolyte is remarkably improved, the half-wave potential (E1 / 2) of the acidic electrolyte in 0.1 M HClO4 reaches 0.835 VRHE, and after 10000 circles of accelerated cyclic voltammetry tests (0.6-1.0 V vs.RHE), the half-wave potential attenuation is less than 5 mV. The peak power density reaches 452 mW cm <-2 > under the condition of hydrogen-air (2 bar back pressure), and the peak power density is increased to 1.0 W cm <-2 > under the condition of hydrogen-oxygen (2 bar back pressure).

Description

Technical Field

[0001] The present invention relates to the field of proton exchange membrane fuel cell materials, and specifically relates to an electrocatalytic oxygen reduction material and its preparation and application. Background Art

[0002] The cathodic oxygen reduction reaction (ORR) of proton exchange membrane fuel cells (PEMFCs) relies on expensive platinum (Pt)-based catalysts, and their high cost has become a bottleneck for commercial applications. On the other hand, Pt-based catalysts are prone to intermediate product adsorption poisoning, metal particle aggregation and dissolution in acidic electrolytes, resulting in insufficient long-term stability. In recent years, non-precious metal catalysts have attracted much attention due to their low cost, and the development of non-precious metal catalysts with high activity and high stability (such as Fe and Co-based materials) has become a hot topic in this field.

[0003] Based on the traditional method of cobalt-based ZIF precursors, due to the too high proportion of microporous structure, the active sites are deeply embedded inside the narrow pores, significantly hindering the reaction mass transfer efficiency; at the same time, metal ions are prone to uncontrollable aggregation during the high-temperature pyrolysis process, forming large-sized particles and the proportion of single-atom active sites is extremely low. In addition, due to the lack of heteroatom coordination regulation, the key reaction intermediates are over-adsorbed, pushing up the reaction energy barrier; in addition, it is difficult for the existing processes to synergistically construct a multi-level catalytic interface of atomically dispersed sites, nanoclusters and dual-atom active centers in a single system, resulting in the lack of cross-scale synergistic effects of electronic structures and reaction paths, seriously restricting the breakthrough of the comprehensive performance of the catalytic system. Summary of the Invention

[0004] Aiming at the deficiencies of the existing technology, the present invention provides an electrocatalytic oxygen reduction material and its preparation and application. By introducing the synergistic effect between Fe clusters and Fe-Co dual-atom sites, the oxygen reduction reaction activity in acidic electrolytes is significantly improved, and its half-wave potential (E 4 ) in 0.1 M HClO 1 / 2 reaches 0.835 V RHE . After 10,000 cycles of accelerated cyclic voltammetry tests (0.6 - 1.0 V RHE ), the half-wave potential decay is less than 5 mV, showing high electrochemical stability.

[0005] One of the technical solutions of the present invention is to provide a preparation method of an electrocatalytic oxygen reduction material, which has the following steps: (1) Prepare a ZnCo-ZIF precursor; (2) Modify the ZnCo-ZIF precursor with phenanthroline; (3) Prepare Co single atoms / nitrogen-doped carbon matrix (Co / NC) by high-temperature pyrolysis; (4) Chemical vapor deposition to load Fe clusters and Fe-Co dual atomic sites, with the gas-phase Fe atom concentration at the critical supersaturation. When the Fe atom concentration reaches the critical supersaturation, it preferentially nucleates at the surface defects or nitrogen-doped sites of Co / NC to form small-sized Fe clusters (Fe AC ). The size of the clusters is limited by the pinning effect of Co single atoms and the confinement effect of the carbon matrix, preventing further growth into nanoparticles.

[0006] Further, the method for preparing the ZnCo-ZIF precursor described in step 1 is as follows: Dissolve 2.82 g of zinc nitrate hexahydrate and 145 mg of cobalt nitrate hexahydrate in 20 mL of methanol to form a metal salt solution; separately dissolve 3.2 g of dimethylimidazole in 40 mL of methanol to form a ligand solution; at room temperature, add the metal salt solution dropwise to the ligand solution, control the stirring rate at 500 rpm, and react for 6 hours; after the reaction, centrifuge, wash with methanol, and vacuum dry at 60 °C for 12 hours to obtain the ZnCo-ZIF precursor.

[0007] Further, the method for modifying ZnCo-ZIF with phenanthroline described in step 2 is as follows: Take 200 mg of the ZnCo-ZIF precursor prepared in step (1) and 50 mg of 1,10-phenanthroline and disperse them in 20 mL of ethanol solution, stir at 300 rpm for 12 hours at 45 °C; after the reaction, directly place it in a vacuum drying oven at 60 °C and dry for 12 hours to obtain the phenanthroline-modified ZnCo-ZIF precursor.

[0008] Further, the method for preparing Co single atoms / nitrogen-doped carbon matrix (Co / NC) by high-temperature pyrolysis described in step 3 is as follows: Place the phenanthroline-modified ZnCo-ZIF precursor prepared in step (2) in a tubular furnace, under an argon atmosphere, program the temperature to rise to 900 °C at a rate of 5 °C / min and keep it calcined for 1 hour; after natural cooling to room temperature, take it out to obtain Co single atoms / nitrogen-doped carbon matrix (Co / NC).

[0009] Further, the method for loading Fe by chemical vapor deposition described in step 4 is as follows: In a chemical vapor deposition (CVD) system, place 15 mg of FeCl 2 powder in the upstream area and 20 mg of the Co / NC material prepared in step (3) in the downstream area; under an argon atmosphere, heat the system to 750 °C at a gas flow rate of 100 mL / min and keep it for 2 hours; after the deposition, naturally cool to room temperature to obtain the material simultaneously loaded with Fe clusters (Fe AC ) and Fe-Co dual atomic sites (FeCo DAsNitrogen-doped carbon-based catalyst; the chemical vapor deposition is carried out in a cavity with an outer diameter of 50 mm, a wall thickness of 3 mm, a length of 600 mm, and an inner diameter of 44 mm.

[0010] The second technical solution of the present invention is to provide an electrocatalytic oxygen reduction material prepared by the above preparation method, which simultaneously loads Fe clusters and Fe-Co dual atomic sites.

[0011] Fe clusters accelerate the charge transfer process by virtue of their local electron enrichment characteristics, and stabilize the dual atomic sites through the "pinning effect", inhibiting the migration or aggregation of metal atoms; at the same time, the electron coupling effect between Fe and Co in the Fe-Co dual atomic sites can precisely regulate the adsorption strength of key oxygen reduction intermediates (such as *OOH, *O), optimize the reaction path and reduce the energy barrier, thereby significantly enhancing the ORR kinetic activity.

[0012] The functional complementarity of the two active sites constructs a multi-scale active center: the clusters provide high-density active sites, while the dual atomic sites enhance the intrinsic activity through an accurate coordination environment. The presence of clusters can disperse the stress of the dual atomic sites, reduce metal dissolution in acidic media, and the nitrogen-doped carbon matrix further improves the overall stability through strong metal-support interactions. In addition, the upward shift of the d-band center of Fe clusters weakens the adsorption strength of intermediates, and synergistically with the orbital hybridization effect of dual atomic sites, optimizes the oxygen molecule dissociation path, promoting an efficient four-electron transfer process; the dynamic interfacial charge redistribution mechanism enables the clusters to balance the oxidation state of the dual atomic sites in real time, inhibiting the peroxidation or protonation inactivation of the active sites, and the pinning effect effectively alleviates the structural collapse under high-temperature and high-potential conditions by anchoring metal atoms, ultimately achieving a synergistic breakthrough in catalytic activity and durability.

[0013] The third technical solution of the present invention is to provide an application of the above electrocatalytic oxygen reduction material in acidic oxygen reduction (ORR) and hydrogen fuel cell cathode materials.

[0014] Advantages of the present invention: (1) The non-precious metal catalyst prepared by the present invention significantly improves the oxygen reduction reaction activity in acidic electrolytes by introducing the synergistic effect between Fe clusters and Fe-Co dual atomic sites. Its half-wave potential (E 4 ) in 0.1 M HClO 1 / 2 reaches 0.835 V RHE . After 10,000 cycles of accelerated cyclic voltammetry tests (0.6 - 1.0 V RHE ), the half-wave potential decay is less than 5 mV, showing high electrochemical stability.

[0015] (2) The cathode of the proton exchange membrane fuel cell with this catalyst exhibits excellent practical performance, with a peak power density of 452 mW cm -2 under hydrogen-air (2 bar back pressure) conditions, and increasing to 1.0 W cm -2 . Description of the Drawings

[0016] Figure 1 are the X-ray diffraction spectra obtained from Example 1, Comparative Example 2, and Comparative Example 3.

[0017] Figure 2 is the transmission electron microscope (TEM) image of Example 1.

[0018] Figure 3 is the energy-dispersive X-ray spectroscopy (EDX) elemental map of Example 1.

[0019] Figure 4 is the aberration-corrected annular dark-field scanning transmission electron microscope image (HAADF-STEM) of Example 1.

[0020] Figure 5 are the linear voltammograms of oxygen reduction for Example 1, Comparative Example 2, and Comparative Example 3 in 0.1 M HClO 4 as the electrolyte.

[0021] Figure 6 are the linear voltammograms of oxygen reduction for Example 1 in 0.1 M HClO 4 as the electrolyte before and after 10,000 cycles.

[0022] Figure 7 are the polarization curve and power density curve of the fuel cell of Example 1 in hydrogen-air.

[0023] Figure 8 are the polarization curve and power density curve of the fuel cell of Example 1 in hydrogen-oxygen.

[0024] Figure 9 are the transmission electron microscope (TEM) images of Comparative Example 3 and Comparative Example 4.

[0025] Figure 10 are the X-ray diffraction spectra of Comparative Example 3 and Comparative Example 4.

[0026] Figure 11 are the linear voltammograms of oxygen reduction for Comparative Example 3 and Comparative Example 4 in 0.1 M HClO 4 as the electrolyte. Detailed Description of the Invention

[0027] The following examples are used to further illustrate the present invention, and the purpose is to explain the present invention rather than to limit the scope of the present invention. Unless otherwise specified, all parts and percentages are by weight.

[0028] The raw materials used in the present invention are all conventional commercially available products unless otherwise specified; the methods used in the present invention are all conventional methods in the art unless otherwise specified.

[0029] The chemical vapor deposition described in the present invention is carried out in a cavity with an outer diameter of 50 mm, a wall thickness of 3 mm, a length of 600 mm, and an inner diameter of 44 mm.

[0030] The following further illustrates the embodiments of the present invention through multiple examples.

[0031] It should be clear that the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts belong to the scope of protection of the present application.

[0032] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a", "the" and "said" used in the embodiments of the present application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. Example 1

[0033] (1) Preparation of ZnCo-ZIF precursor: Weigh 2.82 g of zinc nitrate hexahydrate Zn(NO 3 ) 2 ·6H 2 O and 145 mg of cobalt nitrate hexahydrate Co(NO 3 ) 2 ·6H 2 O, dissolve them in 20 mL of methanol to form a metal salt solution; separately dissolve 3.2 g of dimethylimidazole in 40 mL of methanol to form a ligand solution; at room temperature, drop the metal salt solution into the ligand solution at a constant speed, control the stirring rate at 500 rpm, and continuously react for 6 hours; after the reaction, centrifuge and wash three times with methanol, and then dry in vacuum at 60 °C for 12 hours to obtain the ZnCo-ZIF precursor.

[0034] (2) Ligand modification of ZnCo-ZIF: Take 200 mg of the ZnCo-ZIF prepared in step (1) and disperse it together with 50 mg of 1,10-phenanthroline (Phen) in 20 mL of ethanol solution. Stir at 300 rpm for 12 hours at 45 °C to allow Phen to fully coordinate with ZnCo-ZIF. After the reaction, directly place it in a vacuum drying oven at 60 °C and dry for 12 hours to obtain the Phen-modified ZnCo / Phen composite.

[0035] (3) Preparation of Co single-atom / nitrogen-doped carbon matrix (Co / NC) by high-temperature pyrolysis: Place the ZnCo / Phen composite prepared in step (2) in a tubular furnace. Under an argon atmosphere, program the temperature to rise to 900 °C at a heating rate of 5 °C / min and keep it calcined for 1 hour. After natural cooling to room temperature, take it out to obtain the catalyst, denoted as Co / NC.

[0036] (4) In a chemical vapor deposition (CVD) system, place 15 mg of ferric chloride (FeCl 2 ) powder in the upstream area and 20 mg of Co / NC material in the downstream area. Under an argon atmosphere, heat the system to 750 °C at a gas flow rate of 100 mL / min and keep it for 2 hours to sublime and deposit FeCl 2 on the surface of Co / NC. After the deposition, naturally cool to room temperature to obtain a nitrogen-doped carbon-based catalyst loaded with Fe clusters (Fe AC ) and Fe-Co dual atomic sites (FeCo DAs ), denoted as Fe AC +FeCo DAs / NC. Chemical vapor deposition is carried out in a cavity with an outer diameter of 50 mm, a wall thickness of 3 mm, a length of 600 mm, and an inner diameter of 44 mm. As Figures 1-3 can be seen, there are no nanoparticles in the sample of this example. Co and Fe are loaded on the nitrogen-carbon substrate in the form of single atoms or clusters. Fe AC +FeCo DAs / NC catalyst presents in the shape of a rhombic dodecahedron, and Fe, Co, C, and N are evenly distributed on the NC substrate.

[0037] Figure 4 is the aberration-corrected annular dark-field scanning transmission electron microscopy image (HAADF-STEM) of Example 1. The circles in the figure circle out the Fe clusters, and the squares circle out the FeCo dual atoms, indicating the simultaneous presence of Fe clusters and FeCo dual atoms.

[0038] In saturated O 2 0.1 M HClO 4In solution, the accelerated performance degradation experiment of the Fe AC +FeCo DAs / NC catalyst was carried out at a scanning rate of 200 mV / s in the range of 0.6 V to 1 V. As Figure 6 shown, the half-wave potential of the Fe AC +FeCo DAs / NC catalyst hardly changed before and after 10,000 cycles, indicating good cycle stability. After 10,000 cycles of accelerated cyclic voltammetry tests (0.6 - 1.0 V RHE ), the half-wave potential decay was less than 5 mV.

[0039] As Figure 7 shown, at 80 °C, with a cathode catalyst loading of 3 mg cm -2 , H 2 / air flow rate of 500 / 2000 sccm, 1 bar / 2 bar back pressure test conditions, the maximum power density of the hydrogen-air membrane electrode assembled with the Fe AC +FeCo DAs / NC catalyst was 403 mW cm -2 / 452 mW cm -2 , respectively.

[0040] As Figure 8 shown, at 80 °C, with a cathode catalyst loading of 3 mg cm -2 , H 2 / O 2 flow rate of 500 / 1000 sccm, 1 bar / 2 bar back pressure test conditions, the maximum power density of the hydrogen-oxygen membrane electrode assembled with the Fe AC +FeCo DAs / NC catalyst was 987 mW cm -2 / 1.0 W cm -2 , respectively.

[0041] Comparative Example 1 (1) Preparation of ZnCo-ZIF precursor: Weigh 2.82 g of zinc nitrate hexahydrate Zn(NO 3 ) 2 ·6H 2 O and 145 mg of cobalt nitrate hexahydrate Co(NO 3 ) 2 ·6H 2O was dissolved in 20 mL of methanol to form a metal salt solution; another 3.2 g of dimethylimidazole was dissolved in 40 mL of methanol to form a ligand solution; at room temperature, the metal salt solution was added dropwise to the ligand solution at a constant rate, the stirring rate was controlled at 500 rpm, and the reaction was continued for 6 hours; after the reaction, it was centrifuged and washed three times with methanol, and then dried in vacuo at 60 °C for 12 hours to obtain a ZnCo-ZIF precursor.

[0042] (2)Ligand modification of ZnCo-ZIF: Take 200 mg of the ZnCo-ZIF prepared in step (1) and 50 mg of 1,10-phenanthroline (Phen) and disperse them in 20 mL of ethanol solution, stir at 300 rpm for 12 hours at 45 °C to allow Phen to coordinate fully with ZnCo-ZIF; after the reaction, it was directly placed in a vacuum drying oven at 60 °C and dried for 12 hours to obtain a Phen-modified ZnCo / Phen composite.

[0043] (3)High-temperature pyrolysis to prepare Co single-atom / nitrogen-doped carbon matrix (Co / NC): The ZnCo / Phen composite prepared in step (2) was placed in a tube furnace, and under an argon atmosphere, it was heated at a heating rate of 5 °C / min to 900 °C and calcined at a constant temperature for 1 hour; after natural cooling to room temperature, it was taken out to obtain a Co / NC material with cobalt single atoms dispersed in a nitrogen-doped carbon skeleton.

[0044] Comparative Example 2 The difference in Comparative Example 2 is that Co(NO 3 ) 2 ·6H 2 O was not added to form ZIF-8. ZIF-8 was used instead of ZnCo-ZIF, and the subsequent steps were the same, and finally an Fe / NC Comparative Example 2 sample was prepared.

[0045] Figure 5 This is the oxygen reduction linear voltammogram of Example 1, Comparative Example 2, and Comparative Example 3 in O 2 saturated 0.1 M HClO 4 as the electrolyte. Fe AC +FeCo DAs / NC has the best ORR performance, and the half-wave potential reaches 0.835 V RHE , much higher than Co / NC and Fe / NC. Comparative Example 3

[0046] The difference from Example 1 is that FeCl 2The addition amount was 10 mg. The results showed that the prepared material did not contain clusters. The concentration of Fe atoms in the gas phase was low, and only isolated Fe-Co diatomic sites (FeCo DAs At this time, Fe atoms and Co single atoms form a stable diatomic coordination structure in the nitrogen-carbon matrix through co-doping, but it is not enough to trigger cluster nucleation. The sample is named FeCo DAs / NC. Comparative Example 4

[0047] The difference from Example 1 is that FeCl 2 The addition amount was 20 mg. It was found that the prepared material was large-sized nanoparticles. This is because the excessively high Fe atomic concentration caused the nucleation rate to be much higher than the growth rate, forming a large number of initial nuclei, which then merged into Fe nanoparticles (Fe) through Ostwald ripening at high temperature. NP ). At this time, the pinning effect of Co is broken, and the Fe particles are separated from the diatomic coordination environment to form large-sized nanoparticles.

[0048] FeCl 2 The dosage of FeCl determines the structural characteristics of the product by regulating the gas phase Fe atom concentration and nucleation-growth equilibrium. When the concentration is 15 mg, it is in the critical nucleation condition, and clusters and diatomic sites coexist. 2 The amount of FeO2 will destroy this balance, resulting in the formation of a single structure (diatom or nanoparticle). The sample is named Fe NP +FeCo DAs / NC. Figures 9-10 As shown, for FeCl 2 The deposition amount was regulated, 10 mg and 20 mg FeCl 2 Form FeCo DAs / NC Comparative Example 3 and Fe NP +FeCo DAs / NC comparative example 4, xrd and TEM respectively show that its sample is successfully synthesized.

[0049] Figure 11 The oxygen reduction performance of comparative examples 3 and 4 is 0.78 V and the half-wave potential is 0.78 V respectively. RHE and 0.82V RHE , compared with Example 1, the ORR performance is worse.

[0050] The above embodiments describe in detail the structure, features and effects of the present invention. The above are only preferred embodiments of the present invention. Any changes made in accordance with the concept of the present invention, or modifications to equivalent embodiments with equivalent changes, which do not exceed the scope covered by the specification, should be within the protection scope of the present invention.

Claims

1. A method for preparing an electrocatalytic oxygen reduction material, characterized in that: The following steps are involved: (1) Preparation of ZnCo-ZIF precursor; (2) Phenanthroline modified ZnCo-ZIF precursor; (3) Preparation of Co single atom / nitrogen-doped carbon matrix by high temperature pyrolysis; (4) Chemical vapor deposition loads Fe clusters and Fe-Co diatomic sites, and the gas-phase Fe atomic concentration is at the critical supersaturation.

2. The preparation method according to claim 1, characterized in that: The method for preparing the ZnCo-ZIF precursor in step 1 is as follows: 2.82 g of zinc nitrate hexahydrate and 145 mg of cobalt nitrate hexahydrate were dissolved in 20 mL of methanol to form a metal salt solution; 3.2 g of dimethylimidazole was dissolved in 40 mL of methanol to form a ligand solution; the metal salt solution was added dropwise to the ligand solution at room temperature, the stirring rate was controlled to be 500 rpm, and the reaction was carried out for 6 hours; after the reaction, the mixture was centrifuged, washed with methanol, and vacuum dried at 60 °C for 12 hours to obtain a ZnCo-ZIF precursor.

3. The preparation method according to claim 1, characterized in that: The method for modifying ZnCo-ZIF by phenanthroline in step 2 is as follows: Take 200 mg of the ZnCo-ZIF precursor prepared in step (1) and 50 mg of 1,10-phenanthroline, disperse them in 20 mL of ethanol solution, and stir them at 300 rpm at 45 °C for 12 hours. After the reaction, directly place it in a vacuum drying oven at 60 °C for 12 hours to obtain a phenanthroline-modified ZnCo-ZIF precursor.

4. The preparation method according to claim 1, characterized in that: The method for preparing Co single atom / nitrogen-doped carbon matrix by high-temperature pyrolysis in step 3 is as follows: the phenanthroline-modified ZnCo-ZIF precursor prepared in step (2) is placed in a tube furnace, and in an argon atmosphere, the temperature is raised to 900°C at a heating rate of 5°C / min, and calcined at a constant temperature for 1 hour; after naturally cooling to room temperature, the precursor is taken out to obtain a Co single atom / nitrogen-doped carbon matrix.

5. The preparation method according to claim 1, characterized in that: The method for chemical vapor deposition loading of Fe in step 4 is as follows: in a chemical vapor deposition system, 15 mg of FeCl2 powder is placed in the upstream zone, and 20 mg of the Co / NC material obtained in step (3) is placed in the downstream zone; under an argon atmosphere, the system is heated to 750°C at a gas flow rate of 100 mL / min and maintained for 2 hours; after the deposition is completed, it is naturally cooled to room temperature to obtain a nitrogen-doped carbon-based catalyst that simultaneously loads Fe clusters and Fe-Co diatomic sites.

6. An electrocatalytic oxygen reduction material prepared by the preparation method according to claim 1, characterized in that: Simultaneously load Fe clusters and Fe-Co diatomic sites.

7. Use of the electrocatalytic oxygen reduction material according to claim 6 in acidic oxygen reduction and hydrogen fuel cell cathode materials.

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