CN114122425A - Dioxygen-doped O-FeN4C-O synthesis method and application in fuel cell - Google Patents

Dioxygen-doped O-FeN4C-O synthesis method and application in fuel cell Download PDF

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CN114122425A
CN114122425A CN202111256049.XA CN202111256049A CN114122425A CN 114122425 A CN114122425 A CN 114122425A CN 202111256049 A CN202111256049 A CN 202111256049A CN 114122425 A CN114122425 A CN 114122425A
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doped
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曹达鹏
孙盼盼
谯康伟
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Beijing University of Chemical Technology
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/88—Processes of manufacture
    • H01M4/8878—Treatment steps after deposition of the catalytic active composition or after shaping of the electrode being free-standing body
    • H01M4/8882—Heat treatment, e.g. drying, baking
    • H01M4/8885—Sintering or firing
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/90—Selection of catalytic material
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/10—Fuel cells with solid electrolytes
    • H01M8/1004—Fuel cells with solid electrolytes characterised by membrane-electrode assemblies [MEA]
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/50—Fuel cells

Abstract

Dioxygen-doped O-FeN4A C-O synthesis method and application thereof in fuel cells belong to the technical field of fuel cells. Heme containing carboxyl functional group is added to form a heme-doped ZIF-8 compound with ZIF-8 at room temperature, the carboxyl functional group can migrate to a carbon skeleton during calcination so that an O atom is doped to a second coordination shell layer, and meanwhile, the O atom is coordinated with Fe to form dioxygen-doped O-FeN4C-O; then commercial 40% Pt/C or 60% PtRu/C and dioxygen-doped O-FeN are added4And C-O is respectively used as an anode and a cathode, a GDL or CCM method is adopted to prepare a membrane electrode, and the membrane electrode is finally applied to a proton exchange membrane fuel cell and a hydroxyl exchange membrane fuel cell simultaneously to obtain higher power density.

Description

Dioxygen-doped O-FeN4C-O synthesis method and application in fuel cell
Technical Field
The invention relates to a Fe-N-C catalyst for regulating and controlling O doping, which respectively realizes high power density in a proton exchange membrane fuel cell and a hydroxyl exchange membrane fuel cell by utilizing the unique dioxygen doping effect of the catalyst, and belongs to the technical field of fuel cell application.
Background
With the increasing energy crisis and the increasing urgency of environmental issues, fuel cells are considered as the most promising devices for providing renewable clean energy. The slow kinetics and high overpotential of the cathodic Oxygen Reduction Reaction (ORR) are one of the key bottlenecks in the implementation of this energy technology. Platinum (Pt) -based materials are the most recognized advanced ORR catalysts, but their scarcity, high price, poor methanol/CO tolerance and stability make their large-scale use still very challenging. Therefore, the development of high performance, low cost non-noble metal catalysts for ORR of fuel cells is of great importance.
Isolated M-N ligands in metal-nitrogen-carbon (M-N-C, M metal refers to Fe, Co, Mn, Cu, Ni, etc.) materials have attracted great interest due to their unique electronic properties and high atom utilization efficiency. In particular with FeNxActive site Fe-N-C monatomic catalyst, in particular FeN4The structure, due to its excellent ORR activity, is the most promising candidate catalyst. However, the N atom in Fe-N-C has a strong electronegativity and a strong adsorption capacity to ORR intermediates (e.g., OOH, O, and OH), thereby reducing kinetic activity. The recently reported literature also shows that the intrinsic activity of the metal-nitrogen-carbon structure can be further enhanced by two methods. One is to increase the density of metal active centers, and the other is to adjust the electronic structure of metal centers by doping heteroatoms or adjusting coordination numbers.
Doping electron-withdrawing ligands/atoms (e.g., O-containing groups such as C-OH, C ═ O, C-O-C, and COOH) to the metal center or adjacent carbon can effectively lower the potential barrier, and Ni-O coordinates Ni-N axially4the-O/C sample was able to effectively modulate Ni-N4Electronic structure and reaction kinetics that enhance carbon dioxide reduction (Angew. chem. int. Ed.60,4192-4198 (2021)); axial Fe-O coordinated FeN4The O catalyst not only effectively lowers the formation Energy barrier of the key intermediate COOH ″ (j.am. chem. soc.142,19259-19267), thereby achieving high-efficiency carbon dioxide photocatalytic reduction, but also can increase the electron density, having achieved carbon dioxide reduction over a wide potential range (Energy environ. sci.14,3430-3437 (2021)). During ORR, the Cu-N-C catalyst can generate oxygen reconstruction sites in situ and optimize the electronic structure of Cu atoms, thereby improving ORR activity (Research 2020,1-12 (2020)). Recently, Co-N4Oxygen doping of the second coordination shell has also been shown to effectively modulate the electronic structure and thereby improve catalytic performance (J.Am.chem.Soc.143, 7819-78)27(2021)). Therefore, the research on the O-doped catalyst to enable the O-doped catalyst to have high-activity catalytic activity is of great significance.
The invention uses heme as inorganic iron salt to be cracked with a precursor compound formed by ZIF-8 at high temperature to obtain the Fe-N-C (O-FeN) doped with dioxygen4C-O) catalyst. Reacting O-FeN4C-O is applied to fuel cells. In proton exchange membrane fuel cell testing, the loading was 2.0mg cm-2When the power density reaches 0.88W cm-2Far exceeding O-FeN4C and FeN4C; in the alkaline membrane fuel cell test, the loading was 0.8mg cm-2When the power density reaches 1.24W cm-2Far exceeding O-FeN4C and FeN4C, and even noble metal catalysts.
Disclosure of Invention
The first technical problem to be solved by the invention is to provide a high-performance catalyst suitable for fuel cells, and the obtained dioxygen-doped Fe-N-C (O-FeN) catalyst4C-O) catalyst, which optimizes the electronic structure around monatomic Fe by dioxygen doping and has a mesoporous structure (30-60nm) (example 2, fig. 5), shows excellent cell performance when applied to fuel cell tests.
The prepared dioxygen doped O-FeN4The C-O catalyst is applied to a fuel cell, and in Proton Exchange Membrane Fuel Cell (PEMFC) tests, commercial 40% Pt/C is selected as an anode catalyst to prepare dioxygen-doped O-FeN4And C-O is used as a cathode catalyst, a membrane electrode is prepared by adopting a CCM (continuous current mode) or GDL (GDL) method, and then the cell is assembled and tested. At H2-O2Under the system, the cathode loading is 2.0mg cm-2When the power density reaches 0.88W cm-2(ii) a In a hydroxyl exchange membrane fuel cell test (HEMFC), commercial 60% PtPu/C is selected as an anode catalyst, and prepared dioxygen-doped O-FeN4And C-O is used as a cathode catalyst, a membrane electrode is prepared by adopting a CCM (continuous current mode) or GDL (GDL) method, and then the cell is assembled and tested. At H2-O2Under the system, the cathode loading is 0.8mg cm-2When the power density reaches 1.24W cm-2. Dioxygen-doped O-FeN during two fuel cell testing procedures4The power density of the C-O catalyst battery is far higher than that of O-FeN doped at single oxygen site4C and oxygen-free doped FeN4C catalysts, and even other noble metal catalysts.
The invention relates to dioxygen-doped O-FeN4The C-O synthesis method is characterized by comprising the following steps:
step (1), adopting a metal organic framework ZIF-8 as a carbon precursor, dissolving a certain amount of Zn salt and iron-containing inorganic salt heme in a methanol solution, and performing ultrasonic treatment to obtain a solution A; dissolving a certain amount of 2-methylimidazole in a methanol solution, performing ultrasonic treatment to obtain a solution B, quickly pouring the solution A into the solution B, stirring for 24 hours, centrifuging, washing, and drying in an air-blast drying oven to obtain an iron-containing @ ZIF-8 precursor;
step (2), the precursor containing iron @ ZIF-8 obtained in the step (1) is placed into a calcining furnace, pyrolysis is carried out for 1-6.0h at the high temperature of 1000 ℃ under the inert atmosphere, as the heme contains 2 carboxyl (-COOH) functional groups, the carboxyl functional groups can migrate to a carbon skeleton during the calcining process, so that O atoms are doped to a second coordination shell layer, and meanwhile, the O atoms are also coordinated with Fe, and the Fe-N-C (namely O-FeN) doped with dioxygen sites is finally obtained4C-O) catalyst.
In the step (1), zinc nitrate: the molar ratio of 2-methylimidazole is 2-4: 7.5; the molar ratio of the heme to the zinc nitrate hexahydrate is 0.006: 1-0.045: 1, and the preferable ratio is 0.035: 1.
And (3) introducing inert gas into the high-temperature pyrolysis condition in the step (2) for 0.5-4.0 h, heating to 700-1000 ℃ at the speed of 1-8.0 ℃/min, keeping the temperature for 1-6.0h, and naturally cooling to room temperature. Preferably, the aeration is carried out at room temperature for 1.0h, and then the temperature is raised to 900 ℃ at a temperature raising rate of 5 ℃/min and kept for 2.0 h.
The dioxygen-doped Fe-N-C (i.e. O-FeN) prepared by the invention4C-O) catalyst is of a dodecahedron rhombohedral structure.
The synthesis method for regulating and controlling O doping Fe-N-C and the application thereof in the fuel cell are not only applied to a Proton Exchange Membrane Fuel Cell (PEMFC) but also applied to a Hydroxyl Exchange Membrane Fuel Cell (HEMFC).
PEMFC is applied as follows: the method comprises the steps of selecting commercial 40% Pt/C as an anode catalyst, using an O-doped Fe-N-C catalyst prepared by the method as a cathode catalyst, using Nafion NC-700 as a proton exchange membrane, using Nafion solution as an ionomer, preparing a membrane electrode by a CCM (catalyst coated membrane) method or a GDL (gas diffusion electrode) method, and then using the membrane electrode to assemble a cell for testing a proton exchange membrane fuel cell.
HEMFC was used as follows: the method comprises the steps of selecting commercial 60% PtRu/C as an anode catalyst, using an O-doped Fe-N-C catalyst prepared by the invention as a cathode catalyst, using PAP-TP-85 as a hydroxide exchange membrane, using PAP-TP-85 solution as an ionomer, preparing a membrane electrode by a CCM (catalyst coated membrane) method or a GDL (gas diffusion electrode) method, and then using the membrane electrode to assemble a battery for testing a hydroxide exchange membrane fuel cell. The optimal thickness of the cathode catalyst is 15-20 μm.
The invention has the advantages that:
1. in the process of regulating and controlling the O-doped Fe-N-C catalyst, the double oxygen site is used for doping Fe-N-C (O-FeN)4C-O) catalysts are examples. Because the heme contains 2 carboxyl (-COOH) functional groups, the heme @ ZIF-8-containing precursor is pyrolyzed for 1-6.0h at the high temperature of 1000 ℃ in an inert atmosphere through 700-4C-O) catalyst.
As can be seen from SEM in a of attached figure 1, the iron-containing @ ZIF-8 precursor, namely heme @ ZIF-8 precursor, has a dodecahedron diamond structure. And calcining the obtained dioxygen-doped O-FeN in the SEM picture of b in attached figure 14The morphology of C-O is approximately the same as that of the precursor, which indicates that the structure of the heme @ ZIF-8 precursor is not damaged in the calcining process. As can be seen from FIG. 2, O-FeN4The XRD of C-O has two main broad peaks of 25-44 degrees corresponding to (002) and (101) crystal faces of graphite carbon, and no obvious diffraction peak and metallic iron or Fe are detected by the XRD3C peak, O-FeN4The iron in the C-O catalyst may be present in a monoatomic form. While the TEM diagram of a in FIG. 3 shows O-FeN4No significant particles were present in C-O and the EDS-mapping of b in FIG. 3 demonstrates that C, N, O, Fe elements were uniformly distributed on the carbon skeleton. Fig. 4 further confirms that Fe is distributed in a monoatomic form on the C substrate (small bright spots in the figure) by means of a spherical aberration corrected electron micrograph. From FIG. 5N2The absorption-desorption curve and the pore size distribution curve can show O-FeN4C-O has a typical mesoporous structure (30-60nm), and the existence of the mesoporous structure in the fuel cell is beneficial to mass transfer. As can be seen from the LSV curve (FIG. 6), O-FeN4C-O is 0.5M H2SO4Half-wave potential E in solution1/20.78V, which is significantly higher than O-FeN4C(E1/20.76V) and FeN4C(E1/20.74V); at the same time (FIG. 7), O-FeN4Half-wave potential E of C-O in 0.1M KOH solution1/20.90V, commercial 20% Pt/C (E)1/20.85V) is obviously higher than 50mV and is also higher than O-FeN4C(E1/20.89V) and FeN4C(E1/20.88V), indicating dioxygen-doped O-FeN obtained from heme @ ZIF-84C-O catalysts are more suitable for oxygen reduction reactions under acidic and basic conditions.
2. Testing in a proton exchange membrane fuel cell at H2-O2Under the system, when the loading of the cathode in the MEA is 2.0mg cm-2The current density at a voltage of 0.6V was 0.56A cm at a back pressure of 2.5bar-2The current density at 0.2V was 4.02A cm-2The maximum power density reaches 0.88W cm-2Higher than O-FeN4C(0.74W cm-2) And FeN4C(0.60W cm-2) As cathode catalyst power density.
Testing in a hydroxide exchange membrane fuel cell at H2-O2Under the system, when the loading of the cathode in the MEA is 0.8mg cm-2The current density is 1.08A cm at backpressure of 2.0bar and voltage of 0.65V-2The maximum power density reaches 1.24W cm-2Far exceeds O-FeN4C(0.91W cm-2) And FeN4C(0.79W cm-2) And even exceeds the fuel cell performance of MEAs made from most precious metals.
3. The relationship between the cathode catalyst loading and the catalytic layer thickness was explored and it was noted that for the HEMFC to exhibit optimum performance, the cathode catalytic layer thickness should be controlled to be 15-20 microns.
Drawings
FIG. 1 shows the heme @ ZIF-8 precursor and dioxygen-doped O-FeN of example 14SEM image of C-O catalyst.
FIG. 2 is a schematic diagram of example 1 in which O-FeN is doped at double oxygen sites4XRD spectrum of C-O catalyst.
FIG. 3 is the dioxygen-doped O-FeN of example 14TEM and mapping of C-O catalysts.
FIG. 4 is the dioxygen-doped O-FeN of example 14Spherical aberration electron microscope (HAADF-STEM) for C-O catalyst.
FIG. 5 is the dioxygen-doped O-FeN of example 14C-O catalyst N2Adsorption and desorption isotherms and pore size distributions.
FIG. 6 is the dioxygen-doped O-FeN in example 14C-O catalyst at 0.5M H2SO4LSV curve in solution.
FIG. 7 is the dioxygen-doped O-FeN in example 14LSV profile of C-O catalyst in 0.1M KOH solution.
Fig. 8 is a single cell mold assembled at the time of testing of the fuel cell of example 2.
FIG. 9 shows the results of example 2 in a PEM fuel cell test at H2-O2Under the system back pressure condition of 2.5bar, cathode O-FeN4C-O is 2.0mg cm-2With O-FeN4C and FeN4The I-V curve and the I-P curve of C are compared.
FIG. 10 is a graph of example 2 in a hydroxyl exchange membrane fuel cell test at H2-O2Under the backpressure condition of 2.0bar of the system, the cathode is O-FeN4C-O is 0.8mg cm-2With O-FeN4C and FeN4The I-V curve and the I-P curve of C are compared.
FIG. 11 is a graph of example 2 in a hydroxyl exchange membrane fuel cell test at H2-O2Under the backpressure condition of the system at 2.0bar, different cathodes are O-FeN4C-O carrierI-V curves and I-P curves of the amount, are plotted against each other.
FIG. 12 shows the different cathode O-FeN in the test of the hydroxyl exchange membrane fuel cell of example 24C-O loading vs film thickness.
Detailed Description
The technical solutions of the present invention will be further described in detail with reference to the following specific embodiments and the accompanying drawings, but the present invention is not limited to the following embodiments.
Example 1:
step (1) of preparing heme @ ZIF-8 precursors with different proportions
1) Weighing 0.035mmol of heme and Zn (NO)3)2·6H2Mixing O with certain molar ratio (heme and Zn (NO)3)2·6H2O mole ratio 0.023:2.6, 0.038:2.6, 0.06:2.6, 0.09:2.6, 0.12:2.6) and dissolved in 80mL of anhydrous methanol solution, and ultrasonic treatment is carried out for 10min at room temperature to obtain solution a; weighing 2.463g (30mmol) of 2-methylimidazole, dissolving in 80mL of anhydrous methanol solution, and performing ultrasonic treatment for 10min to obtain solution B; and quickly pouring the solution A into the solution B, stirring at room temperature for 24h, centrifuging the solution (8000r/min,5min), washing with an anhydrous methanol solution for 3 times, collecting, and vacuum-drying in a vacuum drying oven at 70 ℃ for 12h to obtain the heme @ ZIF-8 precursor.
Step (2), selecting heme: zn (NO)3)20.09:2.6 example preparation of dioxygen-doped O-FeN4C-O catalyst
Grinding the product heme @ ZIF-8 precursor obtained in the step (1), placing the ground product into a porcelain ark, placing the porcelain ark into a tube furnace for carbonization, introducing air into the Ar atmosphere at room temperature for 1.0h, heating to 900 ℃ at the speed of 5 DEG/min, keeping the temperature for 2.0h, naturally cooling to room temperature, grinding the carbonized black solid into powder to obtain the dioxygen-doped O-FeN4C-O catalyst. O-FeN4The XDR and TEM images of C-O are shown in FIGS. 2 and 3.
Replacing heme with iron acetylacetonate or iron phthalocyanine, and maintaining Zn (NO) according to the above steps3)2The mol ratio and the synthesis steps are unchanged, and single oxygen site doped is respectively obtainedO-FeN4C. FeN without oxygen site doping4C samples, the activity of the different oxygen-doped catalysts ORR was determined by comparing the LSV curves in acidic and basic solutions, see fig. 6 and 7.
Example 2: dioxygen doped O-FeN4The application of the C-O catalyst in the battery is carried out according to the following steps
Step (1), PEMFC Power Density
Fixing the catalyst in the ink (preferably O-FeN doped at the dioxygen site in example 1)4C-O catalyst): nafion (concentration of solution 5 wt%): isopropyl alcohol (IPA): deionized water (mass ratio) is kept unchanged, Membrane Electrode (MEA) is prepared by a GDL method, the anode adopts commercial 40% Pt/C, and the cathode adopts O-FeN4C-O or O-FeN4C or FeN4C, cathode loading of 2.0mg cm-2. The prepared MEA was combined with a fluorinated ethylene propylene gasket, a gas diffusion layer, having a thickness of 5cm2The graphite bipolar plates and metal collector plates of the flow field assemble the entire acid fuel cell (fig. 8). A fuel cell test system equipped with a backpressure module (Scribner 850e) was used for all fuel cell tests. All gases were 100% humidified, cell test temperature was 80 ℃, back pressure 2.5bar, H2And O2Respectively at a flow rate of 1.0L min-1And 1.5L min-1. In which the dioxygen site is doped with O-FeN4The best C-O performance is achieved, and the power density reaches 0.88W cm-2(FIG. 9).
Step (2), power density of the HEMFC
Fixing the catalyst in the ink (preferably O-FeN doped at the dioxygen site in example 1)4C-O catalyst): isopropyl alcohol (IPA): deionized water (mass ratio) 0.8:40:785.5 (mass ratio) with poly (aryl piperidine), PAP) -terphenyl (terphenyl, TP) -85(85 is N-methyl-4-piperidone/terphenyl monomer molar ratio) (PAP-TP-85): preparing a membrane electrode MEA (membrane electrode assembly) by a CCM (continuous charge-discharge) method, wherein the mass ratio of C in the catalyst is 0.45: 1; the anode is commercial 60% PtRu/C, and the cathode is corresponding O-FeN4C-O or O-FeN4C or FeN4C, cathode loading of 0.8mg cm-2. The prepared membrane electrode (membrane electrode as)Membrane, MEA) was immersed in 3M KOH solution for 2.0h (solution was changed every 1.0 h), the immersed MEA was thoroughly rinsed with deionized water of KOH remaining on the membrane surface, and the rinsed MEA was coupled with a polyperfluoroethylene propylene gasket, gas diffusion layer, having a thickness of 5cm2The graphite bipolar plates and metal collector plates of the flow field assemble the entire alkaline fuel cell unit cell (fig. 8). A fuel cell test system (Scribner 850e) equipped with a back pressure module was used for the fuel cell test. All gases were humidified 100%, cell test temperature 80 ℃, back pressure 2.0bar, H2And O2Respectively at a flow rate of 1.0L min-1And 1.5L min-1. In which the dioxygen site is doped with O-FeN4The C-O performance is best, and the power density reaches 1.24W cm-2(see FIG. 10).
Step (3), testing the power density of MEA (high efficiency Fuel cell) HEMFCs (high efficiency Fuel cell) with different loading amounts of cathodes and measuring the thickness of a catalytic layer
Determination of dioxygen-doped O-FeN4The C-O catalyst has the optimum power density in the HEMFC, and the ratio of isopropyl alcohol (IPA): under the condition that the proportion of deionized water (mass ratio) is not changed to 40:785.5 (mass ratio), cathode O-FeN is prepared by CCM4The C-O loading is 0.5mg cm-2、0.8mg cm-2、1.0mg cm-2、2.0mg cm-2、3.0mg cm-2The anode loading capacity of the MEA membrane electrode is 0.4mg cm -260% PtRu/C. All gases were humidified 100%, cell test temperature 80 ℃, back pressure 2.0bar, H2And O2Respectively at a flow rate of 1.0L min-1And 1.5L min-1(FIG. 11).
Then 0.5mg cm was prepared by CCM-2、0.8mg cm-2、1.0mg cm-2、2.0mg cm-2、3.0mg cm-2The thickness of the catalyst layer is observed by a scanning electron microscope, and the thickness of the cathode catalyst layer sequentially corresponds to 9 micrometers, 15 micrometers, 22 micrometers, 35 micrometers and 43 micrometers (figure 12)
The above-described embodiments are merely examples provided for clearly illustrating the present invention and should not be construed as limiting the claims. The present invention is not limited to the above embodiments, and the specific structure thereof is allowed to vary. All changes which come within the scope of the invention as defined by the independent claims are intended to be embraced therein.
FIG. 1 illustrates that after the heme @ ZIF-8 (FIG. 1a) compound is calcined at high temperature, the dioxygen-doped O-FeN is prepared4The morphology of C-O remains substantially unchanged (FIG. 1b), and is a dodecahedron rhombohedral structure.
FIG. 2 illustrates the dioxygen O-FeN4The XRD of the C-O catalyst has two main broad peaks which are respectively 25-44 degrees and correspond to (002) and (101) crystal faces of graphite carbon, and no obvious diffraction peak and metallic iron or Fe are detected by the XRD3C peak, O-FeN4The C-O catalyst may be present in a monoatomic form.
FIG. 3 illustrates O-FeN doped at dioxygen site4The C-O catalyst TME pattern had no distinct particles, which is consistent with the XRD spectroscopy results in fig. 2, and the mapping pattern indicated that the C, N, O, Fe element was uniformly distributed on the carbon skeleton.
FIG. 4 illustrates dioxygen-doped O-FeN4HAADF-STEM of the C-O catalyst, it can be seen that Fe is distributed on the carbon substrate in a monoatomic form (small bright spots in the figure).
FIG. 5 illustrates dioxygen-doped O-FeN4The C-O catalyst has micropores (1-2nm) and mesopores (30-60nm), and the mesopores are taken as the main components, and the mesoporous structure is favorable for mass transfer in the subsequent fuel cell test process.
FIG. 6 illustrates O-FeN in acidic solution4Half-wave potential of C-O (E)1/20.78V) is obviously higher than O-FeN4C(E1/20.76V) and FeN4C(E1/20.74V), O-FeN is illustrated4C-O dioxygen doping synergistically regulates the electron structure around the monatomic Fe so as to improve the ORR activity.
FIG. 7 illustrates O-FeN in alkaline solution4Half-wave potential of C-O (E)1/20.90V) higher than O-FeN4C(E1/20.89V) and FeN4C(E1/20.88V), O-FeN is illustrated4C-O dioxygen doping synergistically regulates the electron structure around the monatomic Fe so as to improve the ORR activity.
Fig. 8 is a single cell mold assembled at the time of fuel cell testing.
FIG. 9 shows the same loading of cathode in PEMFC 2.0mg cm-2Next, the effect of different catalysts on the power density of PEMFC, it can be seen that O-FeN doped with dioxygen sites4The C-O catalyst has excellent performance in proton exchange membrane fuel cells, and the power density reaches 0.88W cm-2。
FIG. 10 shows the same loading of cathode in HEMFC as 0.8mg cm-2With different catalysts (O-FeN)4C-O、O-FeN4C、FeN4C) The effect on the power density of the HEMFC, O-FeN doped with double oxygen sites can be seen4The C-O catalyst has excellent performance in a hydroxyl exchange membrane fuel cell, and the power density reaches 1.24W cm-2Far exceeding O-FeN4C and FeN4And C, battery performance.
FIG. 11 shows O-FeN doped with dioxygen at cathode in a HEMFC4C-O, the effect of different catalyst loadings on the power density of the HEMFC, it can be seen that the loading is 0.8mg cm-2At a back pressure of 2.0bar, the power density reached the optimum value of 1.24W cm-2。
FIG. 12 shows O-FeN doped with dioxygen sites4The scanning electron microscope images of different cathode loading amounts of C-O show that the thickness of the catalytic layer is increased along with the increase of the loading amount.

Claims (9)

1. Dioxygen-doped O-FeN4The C-O synthesis method is characterized by comprising the following steps:
step (1), adopting a metal organic framework ZIF-8 as a carbon precursor, dissolving a certain amount of Zn salt and iron-containing inorganic salt heme in a methanol solution, and performing ultrasonic treatment to obtain a solution A; dissolving a certain amount of 2-methylimidazole in a methanol solution, performing ultrasonic treatment to obtain a solution B, quickly pouring the solution A into the solution B, stirring for 24 hours, centrifuging, washing, and drying in an air-blast drying oven to obtain an iron-containing @ ZIF-8 precursor;
step (2), the precursor containing iron @ ZIF-8 obtained in the step (1) is placed into a calcining furnace, and is pyrolyzed for 1-6.0h at the high temperature of 1000 ℃ under 700-During the calcination process, the carboxyl functional group can migrate to the carbon skeleton to cause the O atom to be doped to the second coordination shell layer, and meanwhile, the O atom is also coordinated with the Fe to finally obtain the dioxygen-doped Fe-N-C (namely O-FeN)4C-O) catalyst.
2. The dioxygen-doped O-FeN compound of claim 14The C-O synthesis method is characterized in that in the step (1), the ratio of zinc nitrate: the molar ratio of 2-methylimidazole is 2-4: 7.5; the molar ratio of the heme to the zinc nitrate hexahydrate is 0.006: 1-0.045: 1, and the preferable ratio is 0.035: 1.
3. The dioxygen-doped O-FeN compound of claim 14The C-O synthesis method is characterized in that in the step (2), the high-temperature pyrolysis condition is that inert gas is introduced for 0.5-4.0 h at room temperature, then the temperature is raised to 700-1000 ℃ at the speed of 1-8.0 ℃/min, the temperature is kept for 1-6.0h, and the temperature is naturally cooled to room temperature. Preferably, the aeration is carried out at room temperature for 1.0h, and then the temperature is raised to 900 ℃ at a temperature raising rate of 5 ℃/min and kept for 2.0 h.
4. A dioxygen-doped O-FeN prepared by the process of any one of claims 1 to 34C-O。
5. A dioxygen-doped O-FeN prepared by the process of any one of claims 1 to 34C-O, characterized in that the dioxygen site is doped with O-FeN4C-O is a dodecahedron rhombus structure.
6. A dioxygen-doped O-FeN prepared by the process of any one of claims 1 to 34C-O, in fuel cells.
7. Use according to claim 6 in Proton Exchange Membrane Fuel Cells (PEMFC) and in Hydroxyl Exchange Membrane Fuel Cells (HEMFC).
8. Use according to claim 7, in which,PEMFC is applied as follows: commercial 40% Pt/C is selected as an anode catalyst, and O-FeN is doped at double oxygen sites4C-O is used as a cathode catalyst, Nafion NC-700 is used as a proton exchange membrane, Nafion solution is used as an ionomer, a membrane electrode is prepared by a CCM (catalyst coated membrane) method or a GDL (gas diffusion electrode) method, and then the membrane electrode is used for assembling a battery;
HEMFC was used as follows: commercial 60% PtRu/C is selected as anode catalyst, and O-FeN is doped at double oxygen sites4C-O is used as a cathode catalyst, poly (aryl piperidine), PAP-terphenyl (terphenyl, TP) -85(85 is the molar ratio of N-methyl-4-piperidone to terphenyl monomer) (PAP-TP-85) is used as a hydroxide exchange membrane, PAP-TP-85 solution is used as an ionomer, and a membrane electrode is prepared by a CCM (carbon film deposition) method or a GDL (gas diffusion electrode) method and then is used for assembling the battery.
9. Use according to claim 8, in a PEMFC cathode catalyst loading of 2.0mg cm-2(ii) a The cathode catalyst loading capacity of the hydroxyl exchange membrane fuel cell is 0.5-3.0mg cm-2The thickness of the cathode catalytic layer is 15-20 microns.
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