CN113363516A - Catalyst carrier, composite catalyst, preparation method thereof, fuel cell and application thereof - Google Patents

Catalyst carrier, composite catalyst, preparation method thereof, fuel cell and application thereof Download PDF

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CN113363516A
CN113363516A CN202110234515.8A CN202110234515A CN113363516A CN 113363516 A CN113363516 A CN 113363516A CN 202110234515 A CN202110234515 A CN 202110234515A CN 113363516 A CN113363516 A CN 113363516A
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catalyst
particles
composite catalyst
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noble metal
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邵敏华
肖菲
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Hong Kong University of Science and Technology HKUST
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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
    • H01M4/9041—Metals or alloys
    • 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
    • H01M4/8825—Methods for deposition of the catalytic active composition
    • H01M4/8842—Coating using a catalyst salt precursor in solution followed by evaporation and reduction of the precursor
    • 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
    • H01M4/9083—Catalytic material supported on carriers, e.g. powder carriers on carbon or graphite
    • 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
    • H01M4/92—Metals of platinum group
    • H01M4/921—Alloys or mixtures with metallic elements
    • 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
    • H01M4/92—Metals of platinum group
    • H01M4/925—Metals of platinum group supported on carriers, e.g. powder carriers
    • H01M4/926—Metals of platinum group supported on carriers, e.g. powder carriers on carbon or graphite
    • 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

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Abstract

The invention provides a catalyst carrier, a composite catalyst, a method for preparing the composite catalyst and application thereof. The catalyst support comprises a mesoporous carbonaceous matrix doped with at least one non-metallic element selected from groups VA, VIA and VIIA of the periodic Table of the elements, and further comprises active sites dispersed with at least one transition metal monoatomic atom. The transition metal in the catalyst carrier is uniformly dispersed in the carrier by the single-atom active sites, so that the utilization rate of the active sites is improved.

Description

Catalyst carrier, composite catalyst, preparation method thereof, fuel cell and application thereof
Technical Field
The present invention relates to a novel catalyst support, a composite catalyst, a method for preparing the same, a fuel cell and applications thereof, and more particularly, to an Fe-N-C catalyst support, a composite catalyst having oxygen reduction catalytic activity comprising an active support and noble metal (e.g., platinum particles), a method for preparing the same, and applications thereof in a fuel cell, and particularly, to a composite catalyst having fine platinum particles (e.g., platinum particles of 2 to 30nm, preferably 2 to 4 nm) supported on an Fe-N-C support having a large specific surface area, a high degree of graphitization, and a reasonable pore structure, a method for preparing the same, and applications thereof in a fuel cell.
Background
Fuel cell catalysts typically comprise a carbon support and noble metal-based particles (particularly platinum particles). Conventional carbon supports are largely classified into nonporous and porous carbons. Among them, Vulcan carbon, acetylene black and highly graphitized carbon are non-porous carbon, and ketjen black and acetylene oxide black are generally used as porous carbon. However, these carbon carriers are generally susceptible to poisoning by ionomers when used as catalyst carriers, and have problems such as high transport resistance of substances such as oxides or reactive substances (e.g., oxygen)
Attempts have been made to improve the performance of carbon supports. In U.S. Pat. No.6,117,581[1]In (e), Shelef reports a noble metal catalyst supported by a zeolite support containing continuous rich conductor channels. U.S. Pat. No.7,432,221[2]In the Kim and other regulatory vectors, the pore diameter is
Figure BDA0002959397530000011
Thereby reducing poisoning of the oxidation state in the fuel cell. In U.S. Pat. No.8,133,637[3]In the publication, Sun et al report a nanocarbon ring with a high specific surface area and a high degree of graphitization. In U.S. Pat. No.8,278,011[4]Zhu et al introduced a composite carbon support comprising carbon particles and carbon nanowires. In patent application No.2013/148558[5]In the publication, et al report that boron-doped diamond carriers with high specific surface area improve the oxidation resistance of catalysts.
However, these methods require cumbersome preparation and the carbon support still cannot simultaneously achieve high specific area, high graphitization degree, appropriate mesoporous structure and increase the overall oxygen reduction activity of the catalyst.
Thus, there is still a need for a catalyst support comprising active sites while facilitating uniform dispersion of particles for use in preparing a composite catalyst in which the support acts synergistically with the metal catalyst.
Patent documents:
[1]Shelef,Mordecai."Fuel cell electrode comprising conductive zeolite support material."U.S.Patent No.6,117,581.12 Sep.2000.
[2]Kim,Chang-Soo,et al."Electrocatalyst for fuel cells using support body resistant to carbon monoxide poisoning."U.S.Patent No.7,432,221.7 Oct.2008.
[3]Sun,Gongquan,et al."Fuel cells and fuel cell catalysts incorporating a nanoring support."U.S.Patent No.8,133,637.13 Mar.2012.
[4]Zhu,Yimin,et al."Nanostructured catalyst supports."U.S.Patent No.8,278,011.2 Oct.2012.
[5]Minhua Shao,et al."Boron-doped diamond coated carbon catalyst support."U.S.Patent Application No.2013/148,558.
disclosure of Invention
In view of the above technical problems, an object of the present invention is to provide a catalyst support having high oxygen reduction catalytic activity, and a composite catalyst (e.g., noble metal particle-Fe-N-C composite catalyst) comprising the catalyst support and noble metal particles. The catalyst carrier has a high concentration of transition metal (e.g., Fe) single atoms, a high specific surface area and graphitization degree and a suitable mesoporous structure, and can uniformly support a high loading of noble metal particles (particularly, platinum particles) by a simple formic acid reduction method.
Specifically, the present invention provides the following.
1. A catalyst support comprising a mesoporous carbonaceous matrix doped with at least one non-metallic element selected from groups VA, VIA and VIIA of the periodic table of the elements, and further comprising active sites dispersed with at least one transition metal monoatomic atom.
Wherein the non-metallic element is at least one selected from N, S and P, and/or
The transition metal is selected from at least one of Fe, Co and Mn.
Wherein the specific surface area of the catalyst carrier is 1000-1500m2 g-1And/or
The pore diameter of the catalyst carrier is 2-50nm, preferably 4-7 nm.
Wherein the transition metal monoatomic amount is 1 to 5% by weight, preferably 2 to 3% by weight, with respect to the total weight of the catalyst carrier.
Wherein the doping ratio of the non-metal element is 5 to 8 at% and/or the doping ratio of the transition metal is 1 to 5 at% with respect to the total amount of the catalyst carrier.
Wherein the particle size of the catalyst carrier is 50-100 nm.
2. A composite catalyst is characterized by comprising
The catalyst carrier as described in any of the above and
at least one noble metal particle supported on the catalyst support.
Wherein the noble metal is selected from at least one of Pt, Au, Ir, and Ru.
Wherein the loading amount of the noble metal particles is 40 to 50% by weight, preferably 43 to 48% by weight, relative to the total weight of the composite catalyst.
Wherein noble metal particles are uniformly dispersed on the catalyst carrier by a formic acid reduction method,
preferably, the noble metal particles have a particle size of 2 to 30nm, preferably 2 to 4 nm.
3. A method for preparing a composite catalyst, characterized by comprising the steps of:
(1) providing a catalyst support as described in any of the above; and
(2) the noble metal is uniformly supported on the catalyst carrier in the form of particles.
Wherein the step (1) comprises:
(i) synthesizing a metal-organic framework precursor by adopting a metal source containing metal ions or clusters and an organic ligand;
(ii) sintering the metal-organic framework precursor in an atmosphere containing an inert gas and at least one selected from groups VA, VIA and VIIA of the periodic Table of the elements, thereby obtaining the catalyst support.
Wherein the metal source comprises a transition metal ion, preferably Fe, Zn, Cu, or a combination thereof,
optionally, the organic ligand is selected from at least one of 2-methylimidazole, imidazole, 2-ethylimidazole, and 4-azabenzimidazole.
Wherein the step (ii) comprises raising the temperature to 1040 ℃ under an argon atmosphere and keeping the temperature for 30 to 60 minutes; after the temperature is reduced to the room temperature, the temperature is raised to 900-950 ℃ in the argon environment, the ammonia atmosphere is switched and kept for 10-15 minutes, and then the argon is switched and cooled to the room temperature.
Wherein the noble metal is Pt, and the step (2) includes depositing Pt particles on the catalyst support by a formic acid reduction method.
Wherein the formic acid reduction method comprises the steps of reducing platinum particles in an aqueous solution, preferably, during the reduction of the platinum particles, dropwise adding formic acid, keeping the temperature of the solution at 45-50 ℃,
more preferably, the mixed solution after dropping formic acid is maintained at 90-98 ℃ for 60-90 minutes during the reduction of the platinum particles.
Wherein the noble metal is Pt, and the step (2) comprises dispersing the catalyst support into an aqueous solution, adding a Pt source, mixing, heating to 40-50 ℃, then dropwise adding a formic acid solution with a concentration of 30-40 vol%, heating the mixed solution to 90-98 ℃, and keeping for 60-90 minutes, thereby uniformly dispersing Pt particles on the catalyst support.
4. A fuel cell comprising the composite catalyst of any of the above.
5. Use of a composite catalyst as described in any of the above in a fuel cell.
The invention has the advantages of
The invention uses transition metal atom-nonmetal element-mesoporous C containing active sites as a carrier to load noble metal particles for the first time. The invention also utilizes a simple formic acid reduction method to uniformly deposit the noble metal particles in the transition metal atom-nonmetal element-mesoporous C carrier for the first time. In addition, the transition metal is uniformly dispersed in the-nonmetal element-mesoporous C carrier in the form of a single-atom active site, so that the utilization rate of the active site is improved.
The invention also utilizes the synergistic effect between the carrier and the particles to the maximum extent to improve the activity and the stability of the catalyst.
The preparation method of the invention has simple operation and omits the subsequent post-treatment process of the auxiliary agent.
Brief description of the drawings
Figure 1 shows (a) catalytic layer oxygen reduction reaction kinetics and gas, proton mass transfer characteristics prepared from non-porous carbon (where the small gray circles represent low activity platinum particles due to ionomer adsorption); (B) catalytic layer oxygen reduction reaction kinetics and gases made from porous carbon, proton mass transfer characteristics (where small black circles represent platinum particles that cannot participate in the reaction due to too much mass transport resistance) and (C) catalytic layer oxygen reduction reaction kinetics and gases made from reasonable mesoporous carbon, proton mass transfer characteristics (where small black circles represent platinum particles).
FIG. 2 shows a high angle annular dark field high resolution scanning transmission electron micrograph of the catalyst support of example 1-1. White bright spots in the figure indicate uniformly dispersed Fe monoatomic atoms.
FIG. 3 shows a transmission electron micrograph of a composite catalyst prepared according to example 2-1.
FIG. 4 shows the current densities (mA/cm/square centimeter) of the catalysts of example 2-1 and the reference example2) Polarization curve with voltage (volts versus reversible hydrogen electrode, vs RHE). Wherein Pt-Fe-N-C denotes the composite catalyst prepared in example 2-1, TKK Pt/C denotes the catalyst of the reference example, and Pt-Fe-N-C-10 k denotes the catalyst of example 2-1 after 10000 cycles. TKK Pt/C-10 k represents the catalyst of the reference example after 10000 cycles. The catalyst loading of each catalyst on the test electrode is 51ug/cm2。
Fig. 5 shows a transmission electron micrograph of the catalyst particles prepared in example 3.
Detailed Description
Embodiments of the present invention are described in detail below. The embodiments described below are exemplary only, are intended to illustrate the invention, and should not be construed as limiting the invention. The embodiments are not specified to specific techniques or conditions, according to the techniques or conditions described in the literature in the field or according to the product description. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products commercially available.
Definitions and general terms
Reference will now be made in detail to certain embodiments of the invention, examples of which are illustrated by the accompanying structural and chemical formulas. The invention is intended to cover alternatives, modifications and equivalents, which may be included within the scope of the invention as defined by the appended claims. Those skilled in the art will recognize that many methods and materials similar or equivalent to those described herein can be used in the practice of the present invention. The present invention is in no way limited to the methods and materials described herein. In the event that one or more of the incorporated documents, patents, and similar materials differ or contradict this application (including but not limited to defined terminology, application of terminology, described techniques, and the like), this application controls.
It will be further appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. All patents and publications referred to herein are incorporated by reference in their entirety.
The articles "a," "an," and "the" as used herein are intended to include "at least one" or "one or more" unless otherwise indicated or clearly contradicted by context. Thus, as used herein, the articles refer to articles of one or more than one (i.e., at least one) object. For example, "a component" refers to one or more components, i.e., there may be more than one component contemplated for use or use in embodiments of the described embodiments.
The term "active site" refers to a site on a catalyst or catalyst support that participates in a reaction, and is a site where oxygen adsorbs and a reduction reaction occurs.
The term "ionomer" refers to an ionic polymer, such as a Nafion solution, used in the membrane of a fuel cell.
The term "catalyst is homogeneously dispersed on the catalyst support" means that the catalyst particles are distributed on the catalyst support in the nano-state, for example in the form of individual particles of 2-4 nm.
The term "the monoatomic active site is uniformly dispersed in the catalyst carrier" means that the transition metal atom (e.g., Fe atom) on the catalyst carrier is coordinately dispersed in a monoatomic form with the nonmetal element or C in the catalyst carrier. This can be demonstrated from individual white light spots in a scanning transmission electron microscope.
The carbon support for supporting the metal catalyst may include a non-porous carbon support, a porous carbon support and a mesoporous carbon support. The nonporous carbon carrier has high graphitization degree, medium specific surface area, good material transmission efficiency and substrate oxidation resistance. However, the metal catalyst particles supported on the non-porous carbon support are generally distributed on the carbon surface and are easily poisoned by ionomer such as Nafion solution (fig. 1 (a)). In the case of porous carbon, if the pore diameter is too small, it is possible to avoid the ionomer from entering the fine pores to deactivate the metal catalyst particles, but at the same time, the transport resistance of the oxidizing substance is also increased so that the catalyst particles cannot participate in the reaction (fig. 1 (B)). The carbon support having a suitable mesoporous structure can prevent the ionomer from directly contacting the metal catalyst particles while not obstructing the transmission of oxygen (fig. 1 (C)). Carbon supports also affect the stability of fuel cell catalysts. The reason for the poor stability of noble metal (e.g., Au, Pt, etc.) based catalysts is mainly due to the degradation of the electrochemically active area caused by dissolution and agglomeration of noble metal particles. In general, in addition to the instability factors of the catalyst itself, such as too small a particle size, carbon oxidation is a direct cause of dissolution of the noble metal particles. Because agglomeration involves the migration of particles on the surface of the carbon support, higher carbon porosity can reasonably reduce the occurrence of agglomeration.
Based on the above, the present invention provides a catalyst carrier. The catalyst support comprises a mesoporous carbonaceous matrix doped with at least one non-metallic element selected from groups VA, VIA and VIIA of the periodic Table of the elements, and further comprises active sites dispersed with at least one transition metal monoatomic atom.
Preferably, the non-metallic element is selected from at least one of N, S and P. The transition metal may be selected from at least one of Fe, Co, and Mn.
Preferably, the catalyst support of the present invention is a support having a high concentration of transition metal single atoms, a high specific surface area and graphitization degree, and a suitable mesoporous structure. The catalyst support uniformly supports high-loading precious metal (e.g., Au, Pt) particles by a simple formic acid reduction process.
For example, the specific surface area of the catalyst support may be 1000-1500m2g-1. The pore size of the catalyst support may be in the range of from 2 to 50nm, preferably from 4 to 7 nm.
In one example, the content of transition metal single atoms is 1 to 5% by weight, preferably 2 to 3% by weight, relative to the total weight of the catalyst support. The doping ratio of the non-metal element is 5 to 8 atomic% with respect to the total amount of the catalyst carrier. The doping ratio of the transition metal may be 1 to 5 atomic%.
After drying, the catalyst support may be in the form of a fine powder. The particle size of the catalyst support may be 50-100 nm.
The catalyst support may have active sites uniformly distributed, and preferably, transition metal atoms (e.g., Fe atoms) on the catalyst support are coordinately dispersed in a monoatomic form with the non-metal elements or C in the catalyst support. This can be demonstrated from individual white light spots in a scanning transmission electron microscope.
In a preferred embodiment, the catalyst support of the present invention is an Fe-N-C support having a high concentration of Fe single atoms, a high specific surface area and graphitization degree and a suitable mesoporous structure.
Compared with the prior non-noble metal catalyst, the Fe-N-C carrier of the invention has better oxygen reduction activity and stability, thus being used as a proper active carrier for a composite catalyst.
Accordingly, in another aspect, the present invention provides a composite catalyst. The composite catalyst comprises a catalyst support as described in any of the above and at least one noble metal particle supported on the catalyst support.
The noble metal may be selected from at least one of Pt, Au, Ir, and Ru.
The loading of the noble metal particles may be 40 to 50 wt%, preferably 43 to 48 wt%, relative to the total weight of the composite catalyst.
Preferably, the noble metal particles are uniformly dispersed on the catalyst support by a formic acid reduction method, thereby enabling uniform deposition of the noble metal particles, thereby synthesizing a composite catalyst containing abundant active sites, having uniform pores, uniformly dispersed noble metal particles, and excellent activity and stability
Preferably, the noble metal particles supported on the catalyst support have a particle size of 2 to 30nm, preferably 2 to 4 nm.
Preferably, the concentration of Fe single atom of the Fe-N-C carrier in the composite catalyst is 2 to 3% by weight. Further, the Pt particles in the composite catalyst are loaded on Fe-N-C in an aqueous solution by a simple formic acid reduction method, and the loading amount of the Pt is up to 45%.
In yet another aspect, the present invention also provides a method for preparing a composite catalyst, comprising the steps of: (1) providing a catalyst support as described in any of the above; and (2) uniformly supporting a noble metal in the form of particles on the catalyst support.
Preferably, the step (1) comprises:
(i) synthesizing a metal-organic framework precursor by adopting a metal source containing metal ions or clusters and an organic ligand; and
(ii) sintering the metal-organic framework precursor in an atmosphere containing an inert gas and at least one selected from groups VA, VIA and VIIA of the periodic Table of the elements, thereby obtaining the catalyst support.
Wherein the metal source may comprise transition metal ions, preferably Fe, Zn, Cu or combinations thereof,
optionally, the organic ligand is selected from at least one of 2-methylimidazole, imidazole, 2-ethylimidazole, and 4-azabenzimidazole.
Wherein step (ii) may comprise raising the temperature to 1000-1040 ℃ under argon atmosphere for 30-60 minutes; after the temperature is reduced to the room temperature, the temperature is raised to 900-950 ℃ in the argon environment, the ammonia atmosphere is switched and kept for 10-15 minutes, and then the argon is switched and cooled to the room temperature.
In one embodiment, 200-300mg of Fe-doped ZIF-8 precursor was subjected to high temperature pyrolysis, first brought to a temperature of 1000 ℃ under argon atmosphere and held for 30-60 minutes. Cooling to room temperature, heating to 900 deg.C under argon atmosphere, switching ammonia atmosphere, maintaining for 10-15 min, and cooling to room temperature by changing argon. Thus, a black powdery Fe-N-C support was obtained with a yield of 30-50%.
Wherein the noble metal is Pt, and the step (2) includes depositing Pt particles on the catalyst support by a formic acid reduction method.
Wherein the formic acid reduction method comprises the steps of reducing platinum particles in an aqueous solution, preferably, during the reduction of the platinum particles, dropwise adding formic acid, keeping the temperature of the solution at 45-50 ℃,
more preferably, the mixed solution after dropping formic acid is maintained at 90-98 ℃ for 60-90 minutes during the reduction of the platinum particles.
In the case where the noble metal is Pt, the step (2) includes dispersing the catalyst support into an aqueous solution, adding a Pt source, mixing, heating to 40-50 ℃, then dropping a formic acid solution having a concentration of 30-40 vol%, heating the mixed solution to 90-98 ℃, and maintaining for 60-90 minutes, thereby uniformly dispersing Pt particles on the catalyst support.
In one embodiment, the present invention provides a method for preparing a Fe-N-C platinum-supported composite catalyst having high oxygen reduction catalytic activity and stability, comprising the steps of:
zinc nitrate and ferrous sulfate as metal sources and 2-methylimidazole as a ligand are respectively dissolved in a certain amount of methanol solution, oxygen in the solution is removed in an argon environment, and the zinc nitrate and the ferrous sulfate are mixed and stirred at the temperature of 40-45 ℃ to form the Fe-doped ZIF-8 precursor. Excess unreacted metal source and ligand were collected by centrifugation and removed with absolute alcohol, and placed in a vacuum oven for drying. And directly carrying out high-temperature argon and ammonia heat treatment on the precursor to obtain the Fe-N-C carrier.
Uniformly dispersing the heat-treated Fe-N-C in an aqueous solution, and dropwise adding the diluted chloroplatinic acid solution into a carrier solution for uniform mixing. Heating the solution to a certain temperature, slowly dripping a certain amount of formic acid, then heating the mixed solution to a higher temperature, and keeping the temperature for a certain time to completely reduce the platinum source. Excess unreacted platinum source was collected by centrifugation and removed with water and placed in a vacuum oven for drying.
The method utilizes Fe-N-C as a carrier to load platinum particles, not only can improve the active density of the catalyst, but also can solve the defects that the existing method for preparing the noble metal catalyst has low treatment efficiency and needs a complex post-treatment process. In addition, water used as a solvent in the method is simple in synthesis method and beneficial to industrial popularization.
Further, the Fe-N-C carrier is prepared by chelating Fe doped ZIF-8 precursor synthesized by using zinc nitrate and ferrous sulfate as metal sources and 2-methylimidazole as a ligand and sintering at high temperature in the atmosphere of argon and ammonia gas.
Furthermore, the Fe-N-C carrier has high specific surface area and a proper mesoporous structure. For example, the specific surface area of the Fe-N-C support may be 1000-1500m2g-1. The pore size of the mesoporous structure may be 2 to 50nm, preferably 4 to 7 nm.
Further, the high-temperature argon heat treatment of the Fe-N-C carrier comprises the following steps: the temperature is kept at 1000-1040 ℃ and kept for 30-60 minutes under Ar atmosphere.
Further, the high-temperature ammonia gas heat treatment of the Fe-N-C carrier comprises the following steps: heating to 900-950 ℃ under Ar atmosphere, keeping the transamination gas for 10-15 minutes, and cooling to room temperature under argon atmosphere.
Further, the reduction of the platinum particles is carried out in an aqueous solution.
Further, during the reduction of the platinum particles, the temperature of the solution was maintained at 45 to 50 ℃ while dropping formic acid.
Further, during the reduction of the platinum particles, the mixed solution after dropping formic acid was maintained at 90 to 98 ℃ for 60 to 90 minutes.
In yet another aspect, the present invention also provides a fuel cell. A fuel cell may include a cathode, an anode, a proton membrane, a gas diffusion layer, and a bipolar plate. The composite catalyst of the present invention can be used as a catalyst for a cathode and to catalyze the reduction of oxygen to water during the operation of a fuel cell.
The invention also provides the application of the composite catalyst in a fuel cell.
In conclusion, the method utilizes the catalyst carrier containing the active sites to load the noble metal particles such as platinum and the like for the first time, and utilizes the simple formic acid reduction method to uniformly deposit the noble metal particles such as platinum and the like in the catalyst carrier for the first time. In addition, the monoatomic active sites are uniformly dispersed in the catalyst carrier, so that the utilization rate of the active sites is improved. The activity and stability of the catalyst are improved by utilizing the synergistic effect between the carrier and particles to the maximum extent. The preparation method of the invention has simple operation and omits the subsequent post-treatment process of the auxiliary agent.
The present disclosure is further explained or illustrated below by way of examples, which should not be construed as limiting the scope of the present disclosure.
Examples of the present invention
Examples 1 to 1
First, a Fe-doped ZIF-8 support was prepared. 8g of zinc nitrate mixed with 10mg of ferrous sulfate as a metal source and 20g of 2-methylimidazole as a ligand are dissolved in 50mL and 100mL of methanol solutions respectively, oxygen in the solutions is removed by bubbling for 0.5-1h in Ar atmosphere, the two are mixed and stirred at 40 ℃ for 8-10 hours to chelate to form the light gray Fe-doped ZIF-8 precursor. Collecting by centrifugation, washing with anhydrous alcohol for three times to remove excessive unreacted metal source and ligand, and oven drying at 60-70 deg.C for 10-12 hr.
Thereafter, 200mg of the Fe-doped ZIF-8 precursor was pyrolyzed at high temperature, first raised to a temperature of 1000 ℃ under argon atmosphere, and held for 30 minutes. After the temperature is reduced to the room temperature, the temperature is raised to 900 ℃ in the argon environment, the ammonia atmosphere is switched and kept for 10 minutes, and then the argon is changed and the temperature is reduced to the room temperature. Thus, a black powdery Fe-N-C support was obtained with a yield of 30%.
FIG. 2 shows a high resolution scanning transmission electron microscope image of the Fe-N-C carbon support in high angle annular dark field of example 1-1. White bright spots in the figure indicate uniformly dispersed Fe monoatomic atoms. The test method comprises the following steps: the catalyst support powder was characterized in a scanning transmission electron microscope of type "FEI chemis G2" by dispersing it in an ethanol solution and then dropping it onto a copper grid.
The above shows that the catalyst support has transition metal active sites uniformly dispersed in the form of a single molecule.
Examples 1-2-examples 1-5
Catalyst carriers of examples 1-1 to 1-5 were prepared in the same manner as in example 1 except that the preparation conditions were changed in accordance with the parameters shown in the attached Table 1. The yield and form of the obtained catalyst carrier are shown in table 1.
Example 2-1
20mg of the Fe-N-C carrier of example 1-1 was dispersed in 20ml of an aqueous solution. 70mg of chloroplatinic acid hexahydrate are initially diluted with 30mL of aqueous solution and then slowly added dropwise to a stirred solution of Fe-N-C support (30 minutes). Heating the mixed solution to 40 ℃, slowly dropwise adding 10mL of 30-40% formic acid solution (30 minutes), continuously heating the mixed solution to 90-98 ℃, and keeping the temperature for 60-90 minutes. Thus, 30mg of the Fe-N-C platinum-carrying composite catalyst was obtained. The catalyst of this example had a Pt loading of 46 wt% as determined by Inductively Coupled Plasma (ICP) method.
Fig. 3 shows a transmission electron microscope image of the composite catalyst of example 2-1 in which platinum particles are uniformly dispersed on a carbon substrate by formic acid reduction. The test method comprises the following steps: catalyst powder is dispersed in an ethanol solution and then is dripped on a copper net, and characterization is carried out in a transmission electron microscope with the model of JEOL 2010F.
The results showed that the platinum particles were uniformly dispersed on the catalyst carrier in the form of monodisperse nanoparticles of 2 to 4nm without agglomeration into a large particle state.
Examples 2-2-examples 2-5
Composite catalyst supports of examples 2-2 to 2-5 were prepared in the same manner as in example 2-1, except that the preparation conditions were changed in accordance with the parameters shown in the attached Table 2. As a result, the obtained composite catalyst was in the form of black powder, and the yield was 30% to 50%.
These examples all obtained a composite catalyst in which platinum particles were uniformly dispersed on a catalyst support in the form of monodisperse nanoparticles of 2 to 4nm, as shown by transmission electron microscopy observation of "JEOL 2010F".
Example 3
Using Fe-N-C of example 1-1 as a carbon substrate, reduction of platinum particles was carried out by oleylamine and oleic acid organic solution at 190 ℃ to obtain catalyst powder. Fig. 5 shows a transmission electron micrograph of the composite catalyst prepared in this example. As shown in fig. 5, the platinum particles are not uniformly dispersed on the carbon substrate. This demonstrates that the formic acid reduction process in aqueous solution is more effective in uniformly depositing small-sized platinum particles on the Fe-N-C substrate.
Examples 2 to 6
Composite catalyst supports of examples 2-6 were prepared in the same manner as in example 2-1, except that the Fe-N-C support was replaced with the Co-N-C supports of examples 1-4 as shown in Table 3. As a result, the obtained composite catalyst was in the form of black powder, and the yield was 40%.
This example obtained a composite catalyst in which platinum particles were uniformly dispersed on a catalyst support in the form of monodisperse nanoparticles of 2 to 4nm, as observed by a transmission electron microscope of type "JEOL 2010F".
Reference example
A reference example is a commercial Pt/C catalyst available from Tanaka Kikinzoku International (TKK) corporation.
Comparative example 1
Platinum particles were reduced by the same formic acid reduction method using commercial porous ketjen carbon as a substrate. Through the observation of a transmission electron microscope with the model of JEOL 2010F, platinum particles agglomerate to a certain extent under the condition of 40-50% of platinum loading.
Test example 1
The Fe-N-C platinum-carrying catalysts obtained in examples 2-1 and 2-6 were subjected to 0.1M HClO4Electrochemical testing of the solution. The test procedure consisted of dispersing 5mg of catalyst powder in 4mL of isopropanol and 1mL of ultrapure water solution, and adding 20. mu.L of 5% by weight ionomer solution and mixing them homogeneously by ultrasound. And (3) taking a platinum carbon electrode with the diameter of 5mm as a working electrode, dripping 10 mu L of mixed slurry, naturally drying, and respectively taking a carbon rod and Ag/AgCl as a counter electrode and a reference electrode. In an oxygen-saturated solution, the working electrode was swept from 0.125V to 1.0V at a sweep rate of 10mV/s using linear sweep voltammetry at 1600rpm, thereby obtaining the polarization curve of the catalyst. The platinum mass activity of the catalyst at a potential of 0.9V was calculated by the Koutecky-Levich formula:
1/j＝1/j_k+1/j_l
where j is the current density obtained from the test, and j _ l is the limiting current density corresponding to the current density at which the polarization curve in FIG. 4 reaches the plateau. j _ k is the kinetic current density that needs to be calculated, and the value obtained for j _ k relative to the platinum loading on the electrode is the mass activity of platinum. The platinum mass activity of example 2-1 was found to be 0.28A mg by calculation-1Examples 2-6 had a mass activity of 0.23A mg-1Much greater than 0.18A mg of commercial platinum carbon (reference example)-1。
In addition, the platinum catalyst of comparative example 1 had a platinum mass activity of 0.16 to 0.18A mg-1It is not superior to the commercial Pt/C catalyst (reference example).
The above results show that the active carrier plays a crucial role in improving the activity of the composite catalyst
The catalyst of example 2-1 and the catalyst of reference example were each subjected to 0.1M HClO saturated with oxygen4The stability test is carried out in the solution, 10000 cycles (10k) of cycle test is carried out on the working electrode in a potential interval of 0.6-1.0V at a sweep rate of 50mV/s, and the change of the polarization curve of the catalyst is contrastingly analyzed after the initial cycle and the cycle. As a result, as shown in FIG. 4, Pt-Fe-N-C of example 2-1 showed good stability, initial and cyclingThe polarization curves after the loop are basically overlapped; whereas the polarization curve after cycling of the reference example was shifted negatively by 7-10 mV.
Test example 2
Polarization curves of example 2-1, example 1-1 and pure Pt particles under the same conditions were also obtained using the electrochemical test method of test example 1, and their corresponding half-wave potentials (V), i.e., voltages corresponding to half the limiting currents, were calculated, respectively. The results are shown in table 1 below:
TABLE 1
Catalyst type Half-wave potential (V)
Example 2-1(Pt loading 46%) 0.89-0.90
Examples 1-1 (catalyst support) 0.80
Pt particles 0.86
The half-wave potential is an important parameter reflecting the catalytic activity. The above results show that the catalyst activity of example 2-1 is greater than the sum of the expected catalyst activities of the catalyst support + Pt particles, thus demonstrating that synergy occurs between the catalyst support and the Pt particles.
Conclusion
As shown in the above examples and comparative examples, the present invention enables uniform deposition of noble metal particles such as platinum in a catalyst carrier by supporting noble metal particles such as platinum on the catalyst carrier containing active sites. In addition, the monoatomic active sites are uniformly dispersed in the catalyst carrier, so that the utilization rate of the active sites is improved. Moreover, the catalyst carrier and the precious metal particles realize a synergistic effect to improve the activity and the stability of the catalyst.
Figure BDA0002959397530000161
Figure BDA0002959397530000171
Figure BDA0002959397530000181

Claims (19)

1. A catalyst support characterized by comprising a mesoporous carbonaceous matrix doped with at least one non-metallic element selected from groups VA, VIA and VIIA of the periodic table of the elements, and further comprising active sites dispersed with at least one transition metal monoatomic atom.
2. Catalyst support according to claim 1, characterized in that the non-metallic element is selected from at least one of N, S and P, and/or
The transition metal is selected from at least one of Fe, Co and Mn.
3. The catalyst carrier according to claim 1, characterized in that
The specific surface area of the catalyst carrier is 1000-1500m2g-1And/or
The pore diameter of the catalyst carrier is 2-50nm, preferably 4-7 nm.
4. A catalyst support according to any one of claims 1 to 3, characterized in that the transition metal monoatomic amount is 1 to 5% by weight, preferably 2 to 3% by weight, relative to the total weight of the catalyst support.
5. The catalyst carrier according to any one of claims 1 to 4, characterized in that the doping ratio of the non-metallic element is 5 to 8 at% and/or the doping ratio of the transition metal is 1 to 5 at% with respect to the total amount of the catalyst carrier.
6. The catalyst carrier according to any of claims 1 to 5, characterized in that the particle size of the catalyst carrier is 50-100 nm.
7. A composite catalyst is characterized by comprising
The catalyst carrier according to any one of claims 1 to 6 and
at least one noble metal particle supported on the catalyst support.
8. The composite catalyst according to claim 7, characterized in that the noble metal is selected from at least one of Pt, Au, Ir and Ru.
9. The composite catalyst according to any one of claims 7 to 8, characterized in that the loading of the noble metal particles is 40 to 50 wt. -%, preferably 43 to 48 wt. -%, relative to the total weight of the composite catalyst.
10. The composite catalyst according to any one of claims 7 to 9, characterized in that the noble metal particles are uniformly dispersed on the catalyst carrier by a formic acid reduction method,
preferably, the noble metal particles have a particle size of 2 to 30nm, preferably 2 to 4 nm.
11. A method for preparing a composite catalyst, characterized by comprising the steps of:
(1) providing a catalyst support according to any one of claims 1 to 6; and
(2) the noble metal is uniformly supported on the catalyst carrier in the form of particles.
12. The method for producing a composite catalyst according to claim 11, characterized in that the step (1) comprises:
(i) synthesizing a metal-organic framework precursor by adopting a metal source containing metal ions or clusters and an organic ligand;
(ii) sintering the metal-organic framework precursor in an atmosphere containing an inert gas and at least one non-metal element selected from groups VA, VIA and VIIA of the periodic Table of the elements, thereby obtaining the catalyst support.
13. The method for preparing a composite catalyst according to claim 12, characterized in that the metal source comprises transition metal ions, preferably Fe, Zn, Cu or a combination thereof,
optionally, the organic ligand is selected from at least one of 2-methylimidazole, imidazole, 2-ethylimidazole, and 4-azabenzimidazole.
14. The method for preparing a composite catalyst according to claim 12, characterized in that
Said step (ii) comprises raising the temperature to 1000-1040 ℃ under argon atmosphere for 30-60 minutes; after the temperature is reduced to the room temperature, the temperature is raised to 900-950 ℃ in the argon environment, the ammonia atmosphere is switched and kept for 10-15 minutes, and then the argon is switched and cooled to the room temperature.
15. The method of producing a composite catalyst according to claim 11, characterized in that the noble metal is Pt, and the step (2) includes depositing Pt particles on the catalyst support by a formic acid reduction method.
16. The method for preparing a composite catalyst according to claim 15, wherein the formic acid reduction method comprises reducing platinum particles in an aqueous solution, preferably, the temperature of the solution is maintained at 45-50 ℃ while dropping formic acid during the reduction of the platinum particles,
more preferably, the mixed solution after dropping formic acid is maintained at 90-98 ℃ for 60-90 minutes during the reduction of the platinum particles.
17. The method of preparing a composite catalyst according to claim 11, characterized in that the noble metal is Pt, and the step (2) comprises dispersing the catalyst support into an aqueous solution, adding a Pt source, heating to 40-50 ℃ after mixing, then dropping a formic acid solution having a concentration of 30-40 vol%, raising the temperature of the mixed solution to 90-98 ℃, and holding for 60-90 minutes, thereby uniformly dispersing Pt particles on the catalyst support.
18. A fuel cell comprising the composite catalyst of any one of claims 7 to 10.
19. Use of the composite catalyst of any one of claims 7 to 10 in a fuel cell.
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