CN112968185B - Preparation method of plant polyphenol modified manganese-based nano composite electrocatalyst with supermolecular network framework structure - Google Patents

Preparation method of plant polyphenol modified manganese-based nano composite electrocatalyst with supermolecular network framework structure Download PDF

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CN112968185B
CN112968185B CN202110247069.4A CN202110247069A CN112968185B CN 112968185 B CN112968185 B CN 112968185B CN 202110247069 A CN202110247069 A CN 202110247069A CN 112968185 B CN112968185 B CN 112968185B
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CN112968185A (en
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肖高
张梦瑶
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Fuzhou University
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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
    • H01M4/90—Selection of catalytic material
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y40/00—Manufacture or treatment of nanostructures
    • 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
    • H01M4/9016—Oxides, hydroxides or oxygenated metallic salts
    • 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
    • H01M4/9075—Catalytic material supported on carriers, e.g. powder carriers
    • 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

The invention relates to a preparation method of a plant polyphenol modified manganese-based nano composite electrocatalyst with a supermolecular network framework structure, wherein an active substance of a nano material is ZIF-8@ TA-Mn. The problems of the existing fuel cell catalyst are solved, the defects of the prior art, the problems of single precursor obstacle and synthesis cost of the existing fuel cell catalyst are overcome, and the defects of high cost, toxicity and the like of a Pt-based catalytic material are overcome; based on a unique structure of ZIF-8, a metal organic framework nano composite material for a proton membrane fuel cell is developed, and the metal organic framework nano composite material has the advantages of high initial potential, half-slope potential, excellent limiting current, excellent stability, good methanol tolerance, strong methanol poisoning resistance and the like.

Description

Preparation method of plant polyphenol modified manganese-based nano composite electrocatalyst with supermolecular network framework structure
Technical Field
The invention discloses a catalyst for a nano-scale manganese-based oxide proton membrane fuel cell, and relates to a ZIF-8@ TA-Mn nano material prepared by a thermal decomposition process and application of the ZIF-8@ TA-Mn nano material as an oxygen reduction catalyst material.
Background
The proton membrane fuel cell (PEMFC) has the characteristics of high specific energy, low-temperature quick start, convenient operation, high and stable operation, environmental protection and the like, is considered to be an ideal power source for replacing an internal combustion engine, is applied to the aspects of national defense, aerospace, communication, portable power supplies, new energy automobiles and the like, and is concerned by wide scholars. At present, the PEMFC still faces the problems of overhigh cost, short service life and the like, so that the PEMFC cannot be widely applied and further development of the PEMFC in the industrialization process is limited. In order to improve the performance of the PEMFC and reduce the cost of the catalyst, two approaches are mainly used: one is from the intrinsic activity of the catalyst, the use amount of the noble metal Pt is reduced by changing a carrier, preparing an alloy catalyst and the like, so that the activity and the stability of the catalyst are improved; and the other is to improve the performance of the PEMFC by exploring a new membrane electrode preparation method and preparation process from the viewpoint of membrane electrode and catalyst layer structures. The research finds that ZIF-8 is the most widely applied in all ZIFs, and ZIF-8 is Zn2+ZnN formed by using 2-methylimidazole as nitrogen-containing ligand as coordination site4The tetrahedron structure has the characteristics of high specific surface area, special pore structure, three-dimensional network structure, high carbon content and the like (the specific surface area of ZIF-8 is 1900 m)2Per g, pore volume can reach 0.663 cm3/g), so that a plurality of researchers focus on using the ZIF-8-based doped porous carbon material in a fuel cell catalyst, and more particularly, the methylimidazole ligand in the ZIF-8 is very suitable to be used as a precursor due to high nitrogen content. However, in the high-temperature carbonization process of ZIF-8, the ZIF-8 crystal inevitably collapses, so that the prepared catalyst has poor stability, poor methanol toxicity resistance and short service life.
Manganese oxide MnO in contrast to common metal (Fe, Co, Ni) oxidesxHas the characteristics of wide sources, environmental protection, low cost, unique structure, excellent physicochemical properties and the like, is widely concerned, however, manganese oxide has the problems of poor conductivity, low oxygen reduction catalytic activity and the like, the invention takes the conductive material ZIF-8 as a carrier to be compounded with the carrier to improve the electrochemical performance of the carrier, the invention selects a ZIF-8 metal organic framework as a precursor, modifies the ZIF-8 by TA, meanwhile, a mixture of manganese sulfate monohydrate @ TA is added into ZIF-8@ TA to improve the catalytic performance, the ZIF-8@ TA-Mn catalyst is synthesized by a pyrolysis mode, experiments prove that the electrochemical performance of the catalyst can be improved by introducing Mn, the electrochemical performance of the catalyst is changed along with the addition of Mn with different mass, therefore, in the experimental process, the problem to be solved is urgently needed to find the optimal mass ratio of Mn and ZIF-8. The catalyst provided by the invention innovatively introduces the natural adhesion effect of plant polyphenol on metal ions, and the ortho-position phenolic hydroxyl group of tannic acid stably anchors the metal ions in situ, so that the fatal defect that active ingredients are easy to migrate, aggregate and inactivate in the use process of a multi-metal catalyst prepared by a traditional impregnation method is ingeniously overcome, the introduced tannic acid has the anchoring and dispersing effects on active metal particles, the service life of an electrode catalytic material is greatly prolonged, the key problem that the traditional catalyst is few in recycling times is fundamentally broken through, the catalyst is low in price, and the synthesis method is simple and can be used as a promising substitute of a Pt/C catalyst, so that a technical thought is provided for industrial application of the catalyst.
Disclosure of Invention
The invention aims to solve the problems of the existing fuel cell catalyst, overcome the defects of the prior art, solve the problems of single precursor obstacle and synthesis cost of the existing fuel cell catalyst, and overcome the defects of high cost, toxicity and the like of a Pt-based catalytic material; based on the unique structure of ZIF-8, a metal organic framework nano composite material for a proton membrane fuel cell is developed, and the nano composite material has the advantages of high initial potential, half-slope potential, excellent limiting current, excellent stability, good methanol tolerance, strong methanol poisoning resistance and the like.
The invention provides a method for synthesizing a plant polyphenol modified manganese-based nano composite electrocatalyst ZIF-8@ TA-Mn with a supermolecular network framework structure by a simple thermal decomposition preparation process, which comprises the following steps:
(1) weighing 3.3 g of 2-methylimidazole, and dissolving in 70 mL of methanol solution to obtain a 2-methylimidazole solution;
(2) 1.5 g Zn (NO) are weighed out3)2·6H2O dispersing it in 70 mL of methanol solution to obtain Zn2+A solution;
(3) 2-methylimidazole solution is poured rapidly into Zn2+Stirring in the solution at room temperature;
(4) washing the obtained product with a methanol solution, centrifuging, and drying to obtain a ZIF-8 nanocrystal;
(5) dispersing 200 mg of ZIF-8 nanocrystals in 10 mL of deionized water, and carrying out ultrasonic treatment for 5 min to obtain a ZIF-8 solution;
(6) the pH of the TA solution (12 mM, 6 mL) was adjusted to 7.5 with a prepared KOH (6M) solution;
(7) pouring the adjusted TA solution into the ZIF-8 solution, and performing ultrasonic treatment for 30 min to obtain ZIF-8200@ TA solution;
(8) pouring the adjusted TA solution into a manganese sulfate monohydrate solution, and carrying out ultrasonic treatment for 5 min to obtain a manganese sulfate @ TA solution;
(9) finally, the manganese sulfate monohydrate @ TA mixed solution is poured into the prepared ZIF-8200@ TA solution, ultrasonic treatment for 30 min；
(10) Washing the obtained product with deionized water and methanol for several times, and drying to obtain a dried product;
(11) and (3) placing the centrifugally dried product in a (air atmosphere) tube furnace for heat treatment, and naturally cooling to room temperature.
In the technical scheme, the room-temperature stirring time in the step (3) is preferably 24 hours, so that the components are fully mixed;
in the technical scheme, the drying temperature in the step (4) is preferably 80 ℃, and the time is 12 hours;
in the technical scheme, the drying temperature in the step (10) is preferably 60 ℃ and the time is 12 h, so that the deformation of the precursor structure is avoided;
in the technical scheme, the heat treatment temperature in the step (11) is preferably 900 ℃, the reaction time is 3h, and the heating rate is controlled to be 1-5 ℃/min, because the heating rate is too high, the structure collapse is easily caused during calcination.
The ZIF-8@ TA-Mn catalyst prepared at the high temperature of 900 ℃ in argon has a broccoli-shaped morphology structure, wherein the product structure of the ZIF-8 component at the high temperature is carbon particles, Mn exists in the form of oxides, and the final product obtained after the heat treatment of the ZIF-8@ TA-Mn catalyst is known to be manganese oxide (Mn + 2O) and simultaneously have the existence of carbon components compared with an XRD card. The reason why no Zn peak is detected by XRD is that most Zn is volatilized after the Zn is carbonized at high temperature, and a small amount of Zn can be detected in an SEM-EDX element scanning picture.
Compared with commercial Pt/C catalyst, the nano-scale manganese-based oxide proton membrane fuel cell catalyst has the following advantages:
(1) the preparation process of the catalyst adopts a thermal decomposition method with simple equipment, simple operation steps, environmental protection and easily controlled reaction conditions, and not only shows high initial potential, half-slope potential, excellent limiting current, excellent stability and good methanol tolerance, but also has the advantages of strong methanol poisoning resistance and the like.
(2) The initial potential of the prepared ZIF-8@ TA-Mn catalyst is measured in an electrochemical workstation and is relative to a standard hydrogen electrodeCan reach 0.9V comparable to Pt/C, the material has a half slope potential of 0.8V slightly lower than Pt/C, and the catalyst has a greater limiting current density of 5.9 mA cm-2。
(3) The tannic acid TA has rich phenolic hydroxyl structure, so that the tannic acid TA has unique chemical properties, two adjacent phenolic hydroxyl groups of the compound can form a stable five-membered ring chelate with metal ions, the rest phenolic hydroxyl groups do not participate in the reaction, but promote the dissociation of the other two phenolic hydroxyl groups, thereby promoting the formation of the complex, enabling the complex to be more stable, enabling TA-rich catechol hydroxyl groups to have strong adhesion capability, enabling the TA to be adsorbed on the surface of the ZIF-8, thereby generating ZIF nano-crystals with internal reaction sites, in addition, free protons released by TA can continuously destroy coordination bonds of ZIF-8, so that the structure is disintegrated, the alkalescent condition of pH 7.5 can cause partial dissolution of ZIF cores, a little cavity is generated, and a hollow structure is obtained, on the aspect of molecular structure, the nano porous carbon material with a hollow structure can further improve the application performance in the aspect of electrochemistry.
Drawings
FIG. 1 is a graph of the apparent ZIF-8@ TA-Mn prepared;
FIG. 2 is an XRD pattern of ZIF-8@ TA-Mn samples (scan interval: 5-80, step size: 0.02, scan rate: 1.5/min), (a) calcination of blanks at different calcination temperatures (b)900 deg.C and ZIF-8200@TA-Mn200XRD pattern of (a);
FIG. 3 is a scanning electron micrograph of ZIF-8@ TA-Mn;
FIG. 4 is a transmission electron micrograph and a selected area electron diffractogram of ZIF-8@ TA-Mn;
FIG. 5 is a ZIF-8@ TA-Mn initial XPS spectrum survey (a), C (b), Mn (C), N (d);
FIG. 6 is ZIF-8200@ TAx-900 deg.C (x refers to linear cyclic voltammogram at various tannin concentrations (6, 12,18,24 mM)) (scan range-0.9-0.1V, scan rate 10 mv/s);
FIG. 7 shows a ZIF-8@ TA-Mn nanomaterial in N2And O2CV plot in saturated 0.1M KOH (scan range-0.9-0.1V, scan rate 50)mv/s）；
FIG. 8 is a ZIF-8@ TA-Mn nanomaterial prepared at different temperatures in the presence of O2LSV profile in saturated 0.1M KOH (scan range-0.9-0.1V, scan rate 10 mv/s);
FIG. 9 shows ZIF-8@ TA-Mn and Pt/C at O for different Mn loadings2LSV profile in saturated 0.1M KOH (scan range-0.9-0.1V, scan rate 10 mv/s);
FIG. 10 LSV plots of ZIF-8@ TA-Mn at different speeds (speeds 400 rmp, 625 rmp, 900 rmp, 1225 rmp, 1600 rmp, 2025 rmp, scan rate 10 mv/s);
FIG. 11 is a K-L equation plot of ZIF-8@ TA-Mn;
FIG. 12 ZIF-8@ TA-Mn and Pt/C at O2 I-t curves run in saturated 0.1M KOH for long periods of time;
FIG. 13 i-t curves run for ZIF-8@ TA-Mn and Pt/C with methanol addition.
Detailed Description
The invention provides a method for synthesizing a ZIF-8@ TA-Mn catalyst by a simple thermal decomposition preparation process, which comprises the following steps:
(1) weighing 3.3 g of 2-methylimidazole, and dissolving in 70 mL of methanol solution to obtain a 2-methylimidazole solution;
(2) 1.5 g Zn (NO) are weighed out3)2·6H2O dispersing it in 70 mL of methanol solution to obtain Zn2+A solution;
(3) 2-methylimidazole solution is poured rapidly into Zn2+Stirring in the solution at room temperature;
(4) washing the obtained product with a methanol solution, centrifuging, and drying to obtain a ZIF-8 nanocrystal;
(5) dispersing 200 mg of ZIF-8 nanocrystals in 10 mL of deionized water, and carrying out ultrasonic treatment for 5 min to obtain a ZIF-8 solution;
(6) the pH of the TA solution (12 mM, 6 mL) was adjusted to 7.5 with a prepared KOH (6M) solution;
(7) pouring the adjusted TA solution into the ZIF-8 solution, and performing ultrasonic treatment for 30 min to obtain ZIF-8200@ TA solution;
(8) pouring the adjusted TA solution into a manganese sulfate monohydrate solution, and carrying out ultrasonic treatment for 5 min to obtain a manganese sulfate @ TA solution;
(9) finally, the manganese sulfate monohydrate @ TA mixed solution is poured into the prepared ZIF-8200Ultrasonic treating in @ TA solution for 30 min;
(10) washing the obtained product with deionized water and methanol for several times, and drying to obtain a dried product;
(11) and (3) placing the centrifugally dried product in a (air atmosphere) tube furnace for heat treatment, and naturally cooling to room temperature.
In the technical scheme, the stirring time of the step (3) at room temperature is preferably 24 hours, so that the components are fully mixed;
in the technical scheme, the drying temperature in the step (4) is preferably 80 ℃, and the time is 12 hours;
in the technical scheme, the drying temperature in the step (10) is preferably 60 ℃, the time is 12 hours, and the deformation of the precursor structure is avoided;
in the technical scheme, the heat treatment temperature in the step (11) is preferably 900 ℃, the reaction time is 3h, and the heating rate is controlled to be 1-5 ℃/min, because the heating rate is too high, the structure collapse is easily caused during calcination.
The invention provides a nano-scale manganese-based oxide material and an oxygen reduction catalyst using the material.
The active substance is abbreviated as ZIF-8@ TA-Mn.
The ZIF-8@ TA-Mn catalyst is prepared by thermal decomposition.
The invention uses a platinum electrode as a counter electrode, a saturated silver chloride electrode (Ag/AgCl) as a reference electrode and a Pt/C electrode as a working electrode.
The concentration of Nafion added in the preparation process of the catalyst ink was 5wt%, and the amount used was 15 ul.
A catalyst ink (ink) was prepared by dispersing 4 mg of the catalyst of the present invention in 1 mL of a mixed solution (250. mu.L of deionized water, 735. mu.L of isopropyl alcohol and 15. mu.L of a 5wt% Nafion solution) using a scale. Then gradually dropping 28 μ L ink to the glassy carbonElectrode surface (catalyst loading 0.25 mg cm-2) And carrying out an electrocatalysis performance test after naturally drying.
All electrocatalytic performance tests described in the present invention were performed in 0.1M KOH (pH = 13.62) electrolyte, and the experimentally measured potential was converted to a potential relative to a Reversible Hydrogen Electrode (RHE) by the following formula:
Figure DEST_PATH_IMAGE002
the potential values referred to in the present invention are all potentials relative to the reversible hydrogen electrode.
The catalyst of the present invention requires CV activation for 3 cycles before electrochemical testing.
The catalyst is tested at normal temperature, and the influence of large temperature change difference on the performance of the catalyst is prevented.
The invention will be further illustrated with reference to the following specific examples. In order to further clarify the present invention, preferred embodiments of the present invention are described in connection with the examples which are intended to illustrate various features and advantages of the present invention, but not to limit the scope of the invention which is not defined by the claims. In addition, it should be understood that various changes or modifications can be made by those skilled in the art after reading the disclosure of the present invention, and such equivalents also fall within the scope of the invention.
The experimental methods used in the following examples are all conventional methods unless otherwise specified; reagents, materials and the like used in the following examples are commercially available unless otherwise specified.
Example 1:
the embodiment shows a synthesis method of a ZIF-8@ TA-Mn catalyst, which comprises the following steps:
(1) weighing 3.3 g of 2-methylimidazole, and dissolving in 70 mL of methanol solution to obtain a 2-methylimidazole solution;
(2) 1.5 g Zn (NO) are weighed out3)2·6H2O dispersing it in 70 mL of methanol solution to obtain Zn2+A solution;
(3) 2-methylimidazole solution is poured rapidly into Zn2+Stirring in the solution at room temperature;
(4) washing the obtained product with a methanol solution, centrifuging, and drying to obtain a ZIF-8 nanocrystal;
(5) dispersing 200 mg of ZIF-8 nano crystals in 10 mL of deionized water, and performing ultrasonic treatment for 5 min to obtain ZIF-8200A solution;
(6) the pH of the TA solution (12 mM, 6 mL) was adjusted to 7.5 with a prepared KOH (6M) solution;
(7) pouring the adjusted TA solution into the ZIF-8 solution, and performing ultrasonic treatment for 30 min to obtain ZIF-8200@ TA solution;
(8) weighing 200 mg of manganese sulfate monohydrate, and dispersing the manganese sulfate monohydrate in 10 mL of deionized water to obtain a manganese sulfate monohydrate solution;
(9) pouring the adjusted TA solution into a manganese sulfate monohydrate solution, and carrying out ultrasonic treatment for 5 min to obtain a manganese sulfate monohydrate @ TA solution;
(10) finally, the manganese sulfate monohydrate @ TA mixed solution is poured into the prepared ZIF-8200Ultrasonic treating in @ TA solution for 30 min;
(11) washing the obtained product with deionized water and methanol for several times, and drying to obtain a dried product;
(12) placing the centrifugally dried product in a (air atmosphere) tube furnace for heat treatment at 700 ℃, 800 ℃ and 900 ℃, and naturally cooling to room temperature to respectively obtain ZIF-8200@TA-Mn200-700℃、ZIF-8200@TA-Mn200-800℃、ZIF-8200@TA-Mn200-900℃。
In the technical scheme, the stirring time of the step (3) at room temperature is preferably 24 hours, so that the components are fully mixed;
in the technical scheme, the drying temperature in the step (4) is preferably 80 ℃, and the time is 12 hours;
in the technical scheme, the drying temperature in the step (11) is preferably 60 ℃ and the time is 12 h, so that the deformation of the precursor structure is avoided;
in the technical scheme, the reaction time of the heat treatment temperature in the step (12) is 3h, and the heating rate is controlled at 5 ℃/min, because the heating rate is too high, the structure collapse is easily caused during calcination.
ZIF-8200-900 ℃ preparation process:
(1) weighing 3.3 g of 2-methylimidazole, and dissolving in 70 mL of methanol solution to obtain a 2-methylimidazole solution;
(2) 1.5 g Zn (NO) are weighed out3)2·6H2O dispersing it in 70 mL of methanol solution to obtain Zn2+A solution;
(3) 2-methylimidazole solution is poured rapidly into Zn2+Stirring in the solution at room temperature;
(4) washing the obtained product with a methanol solution, centrifuging, and drying to obtain a ZIF-8 nanocrystal;
(5) dispersing 200 mg of ZIF-8 nano crystal in 10 mL of deionized water, and carrying out ultrasonic treatment for 5 min to obtain ZIF-8200A solution;
(6) the resulting ZIF-8200Washing the solution with deionized water and methanol for several times, and drying at 60 ℃ to obtain a dried product;
(7) the product is put into a (air atmosphere) tube furnace for heat treatment at 900 ℃, and then is naturally cooled to room temperature to obtain ZIF-8200-900℃。
ZIF-8200@ TAx-900 ℃ preparation (x refers to different tannin concentrations (6, 12,18,24 mM)):
(1) weighing 3.3 g of 2-methylimidazole, and dissolving in 70 mL of methanol solution to obtain a 2-methylimidazole solution;
(2) 1.5 g Zn (NO) are weighed out3)2·6H2O dispersing it in 70 mL of methanol solution to obtain Zn2+A solution;
(3) 2-methylimidazole solution is poured rapidly into Zn2+Stirring in the solution at room temperature;
(4) washing the obtained product with a methanol solution, centrifuging, and drying to obtain a ZIF-8 nanocrystal;
(5) dispersing 200 mg of ZIF-8 nano crystal in 10 mL of deionized water, and carrying out ultrasonic treatment for 5 min to obtain ZIF-8200A solution;
(6) the pH value of TA solution (6 mL) with the concentration of 6,12,18 and 24 mM is adjusted to 7.5 by using prepared KOH (6M) solution;
(7) respectively pouring the adjusted TA solution into the ZIF-8 solution, and performing ultrasonic treatment for 30 min to obtain ZIF-8200@ TAx solution (x is different tannin concentrations (6, 12,18,24 mM));
(8) washing the obtained product with deionized water and methanol for several times, and drying at 60 ℃ to obtain a dried product;
(9) the product is put into a (air atmosphere) tube furnace for heat treatment at 900 ℃, and then is naturally cooled to room temperature to obtain ZIF-8200@TAx-900℃。
FIG. 1 is ZIF-8 prepared200@TA-Mn200-900 ℃ appearance.
Phase identification and microstructure and structure characterization of the ZIF-8@ TA-Mn material obtained in the example were carried out: and phase identification is carried out on the prepared material by using a powder X-ray diffractometer and an X-ray photoelectron spectrometer, and the microscopic morphology and the structural characterization are carried out on the obtained material by using a scanning electron microscope and a transmission electron microscope.
FIG. 2 XRD patterns (a) of ZIF-8@ TA-Mn samples at different calcination temperatures (700 deg.C, 800 deg.C, 900 deg.C), XRD patterns (b) of ZIF-8 and ZIF-8@ TA-Mn calcined at 900 deg.C (scan interval: 5 ° -80 °, scan rate: 8 °/min). No zinc ion was detected at a calcination temperature of 800 ℃ or higher, demonstrating ZIF-8200@TA-Mn200Most of the zinc ions are removed during carbonization at high temperature. As can be seen from the figure, the purity of the sample is very high, no obvious impurity is generated, and the synthesized material has good crystallinity as the diffraction peak is sharper, so that the ZIF-8@ TA-Mn complex is successfully obtained.
FIG. 3 and FIG. 4 are ZIF-8, respectively200@TA-Mn200-900 ℃ scanning electron micrograph, transmission electron micrograph and selected area electron diffraction pattern. As can be seen from the figure, the ZIF-8@ TA-Mn sample powder is composed of a group of particles having non-uniform sizes and irregular shapesIn the middle, there is a little cavity. SEM-EDX element scanning is carried out on the catalyst, wherein the contents of C, Mn and Zn elements are 84%, 7% and 1% respectively. The relatively small content of Zn element indicates that Mn and a small amount of Zn element are present on the surface of the catalyst. The particle size distribution is 100 nm-30 nm, the lattice spacing is 0.222 nm, 0.256nm and 0.33nm, and the catalyst is favorable for enhancing the catalytic action of the catalyst. Corresponding to the (200) and (111) crystal planes of Mn +2O and the (002) crystal plane of graphitic carbon, indicate that Mn oxide nanoparticles are embedded in graphitic carbon layers and that the edges are exposed rather than the entire basal plane. It is proved that tannic acid becomes C to wrap the outer layer of the catalyst after being calcined.
FIG. 5 is ZIF-8200@TA-Mn200-900 ℃ XPS spectrum full spectrum (a), C spectrum (b), Mn spectrum (C), N spectrum (d); where the C — O structure is believed to be beneficial in facilitating ORR progression in alkaline electrolytes. Meanwhile, pyridine N is beneficial to initial potential correction in the catalytic process, graphitized N in an alkaline electrolyte has an important effect on oxygen reduction reaction, the existence of graphitized N is beneficial to increase of current density, the electronic structure on the surface of the graphite carbon layer can be changed, and the catalytic effect on the reduction process of the oxygen reduction reaction is good.
Example 2:
this example shows an electrochemical performance study using nanomaterial ZIF-8@ TA-Mn as a catalyst.
The invention uses a platinum electrode as a counter electrode, a saturated silver chloride electrode (Ag/AgCl) as a reference electrode and a Pt/C electrode as a working electrode.
A catalyst ink (ink) was prepared by dispersing 4 mg of the catalyst of the present invention in 1 mL of a mixed solution (250. mu.L of deionized water, 735. mu.L of isopropyl alcohol and 15. mu.L of a 5wt% Nafion solution) using a scale. Then gradually dripping 28 mu L of ink on the surface of the glassy carbon electrode (the loading amount of the catalyst is 0.25 mg cm & lt-2 & gt), and carrying out an electro-catalytic performance test after naturally airing.
All electrocatalytic performance tests described in the present invention were performed in 0.1M KOH (pH = 13.62) electrolyte, and the experimentally measured potential was converted to a potential relative to a Reversible Hydrogen Electrode (RHE) by the following formula:
Figure DEST_PATH_IMAGE004
the potential values referred to in the present invention are all potentials relative to the reversible hydrogen electrode.
The catalyst of the present invention requires CV activation for 3 cycles before electrochemical testing.
The catalyst is tested at normal temperature, and the influence of large temperature change difference on the performance of the catalyst is prevented.
Nafion added in the preparation process of the catalyst is produced by Aldrich sigma company, and the concentration is 5%.
The catalyst is absorbed by a pipette gun to be 7 ul and dropped on a working electrode, the step is repeated for 3 times after the catalyst is naturally aired, then the working electrode slowly enters 0.1M KOH electrolyte saturated by oxygen, bubbles are prevented from being generated on the working electrode in the step, and the electrolyte is continuously introduced into oxygen in the whole testing process to ensure oxygen saturation.
Cyclic voltammetry and linear cyclic voltammetry tests were performed on the catalyst obtained in this example: the cyclic voltammetry test was carried out using an electrochemical workstation manufactured by Pine of the United states, the test voltage sweep range was-0.9-0.1V, the sweep rate was 50 mV/s, and during the test, the cyclic voltammetry test was carried out after 3 cycles of activation with a current density of 50 mV/s. Linear cyclic voltammetry tests were also performed using the Pine electrochemical workstation, with a test voltage sweep range of-0.9-0.1V and a sweep rate of 50 mV/s. The current density of the catalyst material under different rotating speeds can be obtained through rotating speed test, the number of transferred electrons can be obtained by utilizing a K-L equation, the test current density is 10mV/s, and the rotating speeds are 400 rmp, 625 rmp, 900 rmp, 1225 rmp, 1600 rmp and 2025 rmp. The stability and the methanol tolerance are also important indexes of the catalyst performance, the test is also completed on an electrochemical workstation, the stability test voltage is-0.189V, and the test time length is 20000 s; the methanol tolerance test voltage was-0.189V, the test duration was 1000 s, and a 2M methanol solution was dropped at 250 s.
FIG. 6 is ZIF-8200@ TAx-900 deg.C (x means different tannic acid concentrations (6, 12,18,24 mM)) linear cyclic voltammogram (test voltage range: -0.9-0.1V, scanning speed: 10 mV/s), experimental finding that ZIF-8 was found at a tannic acid solution concentration of 12mM200The catalyst performance is highest at @ TA-900 ℃, and the limiting current and the initial current are both larger than those of catalysts with other concentrations. The concentration of tannic acid adopted by the invention is 12mM, the pH value is 7.5 alkalescence, the prepared tannic acid solution is introduced into the ZIF-8 solution, the tannic acid solution and the manganese sulfate monohydrate solution are fused and stirred to generate a stable complex, and the complex product is combined with ZIF-8@ TA for reaction and is subjected to heat treatment to finally generate the catalyst ZIF-8@ TA-Mn.
FIG. 7 is ZIF-8200@TA-Mn200The curve diagram of the cyclic voltammetry characteristic of the catalyst at 900 ℃ (the test voltage sweep range is between-0.9 and 0.1V, the sweep speed is 50 mV/s), the CV curve of the sample ZIF-8@ TA-Mn has no obvious peak value in a 0.1M KOH solution saturated by nitrogen, and the CV curve under the oxygen saturation condition has an obvious redox peak when the potential is 0.68V (vs. RHE) when the test environment is saturated by oxygen, which indicates that the sample ZIF-8@ TA-Mn has obvious catalytic activity on oxygen reduction.
FIG. 8 is a linear cyclic voltammogram of the ZIF-8@ TA-Mn catalyst at different temperatures (test voltage range: -0.9-0.1V, scan rate: 10 mV/s), respectively, with the ZIF-8@ TA-Mn catalyst performing best when the calcination temperature is 900 ℃.
FIG. 9 is a ZIF-8@ TA-Mn and Pt/C at O for different Mn loadings2An LSV diagram in saturated 0.1M KOH (the scanning range is-0.9-0.1V, the scanning speed is 10 mv/s), when the mass ratio of ZIF-8/Mn is 1:1, the catalyst ZIF-8@ TA-Mn has excellent performance, and the initial potential and the half-slope potential of the material are respectively 0.9V and 0.8V and are slightly lower than Pt/C. But the material has a greater limiting current density of 5.9 mA cm than Pt/C-2. This indicates that the introduction of Mn significantly improves the oxygen reduction activity of the catalyst and that the ORR activity tends to increase and then decrease as the Mn content increases. This is as we start to predict if ZIF is usedThe catalyst obtained by calcination of-8 shows a certain catalytic activity, but the activity is relatively low. When tannin is introduced into the precursor ZIF-8 and a certain amount of manganese sulfate monohydrate is added, the activity of the obtained catalyst ZIF-8@ TA-Mn is greatly improved.
FIG. 10 shows the catalyst ZIF-8 at different speeds (400 rmp, 625 rmp, 900 rmp, 1225 rmp, 1600 rmp, 2500 rmp)200@TA-Mn200The LSV curve at-900 deg.C (scan speed: 10 mV/s) shows a tendency to increase gradually with increasing rotation speed, mainly due to the fact that the increasing rotation speed effectively shortens the diffusion layer of the oxygen reduction reaction. A series of oxygen reduction curves of the catalyst show a better diffusion-limiting current platform, which means that the catalytic active sites of the catalyst are distributed more uniformly, and the speed of the oxygen reduction process is improved.
FIG. 11 is ZIF-8200@TA-Mn200The slope of the K-L curve at 900 ℃ remains substantially constant over the entire potential range, which indicates that the oxygen reduction reaction has the same number of transferred electrons at different potentials over the catalyst. The resulting catalyst was shown to have an electron transfer number of 3.7, indicating that the reaction process followed a 4-electron mechanism.
FIG. 12 is a ZIF-8 test by chronoamperometry200@TA-Mn200-900 ℃ and Pt/C, the initial current density of the Pt/C catalyst lost significantly 23% after testing for 20000 s, while the ZIF-8@ TA-Mn catalyst decreased only 12%, indicating that the catalyst has better stability than the commercial Pt/C catalyst.
FIG. 13 is ZIF-8200@TA-Mn200Methanol resistance plots for the ZIF-8@ TA-Mn and commercial 20% Pt/C catalysts, measured using an i-t technique with 2M methanol added to 0.1M KOH electrolyte at 300s, no effect other than a slight change in the ZIF-8@ TA-Mn current density was observed, whereas the Pt/C catalysts exhibited a significant change in current density due to methanol oxidation. These show that methanol poisons Pt/C and loses part of its catalytic activity, and that the surface ZIF-8@ TA-Mn is also clear in terms of resistance to methanol toxicityDue to Pt/C.
The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiment. Any modification, equivalent replacement, or improvement made without departing from the spirit and principle of the present invention shall fall within the protection scope of the present invention.

Claims (2)

1. The preparation method of the plant polyphenol modified manganese-based nano composite electrocatalyst with a supermolecular network framework structure is characterized by comprising the following steps of: the preparation method comprises the following steps:
(1) dissolving 2-methylimidazole in a methanol solution;
(2) adding Zn (NO)3)2·6H2O is dispersed in the methanol solution;
(3) quickly pouring the 2-methylimidazole solution obtained in the step (1) into the Zn obtained in the step (2)2+The solution was stirred at room temperature for 24 hours;
(4) washing the obtained product with a methanol solution, centrifuging, and finally drying at 80 ℃ to obtain a ZIF-8 nanocrystal;
(5) dispersing the ZIF-8 nanocrystals in deionized water, and performing ultrasonic treatment for 5 min to obtain a ZIF-8 solution;
(6) adjusting the pH value of the TA solution to 7.5 by using KOH solution;
(7) pouring the adjusted TA solution into the ZIF-8 solution, and carrying out ultrasonic treatment for 30 min to obtain a ZIF-8@ TA solution;
(8) pouring the adjusted TA solution into a manganese sulfate solution, and carrying out ultrasonic treatment for 5 min to obtain a manganese sulfate @ TA solution;
(9) finally, pouring the manganese sulfate @ TA solution into the ZIF-8@ TA solution, and carrying out ultrasonic treatment for 30 min;
(10) washing the obtained product with deionized water and methanol for several times, and drying to obtain a dried product;
(11) placing the dried product in a tubular furnace in an air atmosphere for heat treatment, and then naturally cooling to room temperature to obtain the plant polyphenol modified manganese-based nano composite electrocatalyst ZIF-8@ TA-Mn with a supermolecular network framework structure;
the drying temperature in the step (10) is 60 ℃, and the time is 12 hours;
the heat treatment temperature in the step (11) is 900 ℃, the reaction time is 3 hours, and the heating rate is controlled to be 1-5 ℃/min;
the concentration of the KOH solution in the step (6) is 6M;
the concentration of the TA solution in step (6) was 12 mM.
2. The plant polyphenol modified manganese-based nanocomposite electrocatalyst with supramolecular network framework structure prepared by the preparation method of claim 1.
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