CN113285079A - Double-heteroatom-doped CoFe/SNC composite material and preparation and application thereof - Google Patents

Double-heteroatom-doped CoFe/SNC composite material and preparation and application thereof Download PDF

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CN113285079A
CN113285079A CN202110431056.2A CN202110431056A CN113285079A CN 113285079 A CN113285079 A CN 113285079A CN 202110431056 A CN202110431056 A CN 202110431056A CN 113285079 A CN113285079 A CN 113285079A
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snc
cofe
composite material
heteroatom
double
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李巧霞
李林科
谢胜男
陈溢
刘峰
朱志强
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Shanghai University of Electric Power
Shanghai Electric Power University
University of Shanghai for Science and 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
    • H01M4/8825—Methods for deposition of the catalytic active composition
    • 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
    • H01M4/90—Selection of catalytic material
    • H01M4/9075—Catalytic material supported on carriers, e.g. powder carriers
    • 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
    • H01M2004/8678—Inert electrodes with catalytic activity, e.g. for fuel cells characterised by the polarity
    • H01M2004/8689—Positive electrodes
    • 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 double-heteroatom-doped CoFe/SNC composite material and preparation and application thereof, wherein the preparation method specifically comprises the following steps: (a) uniformly dispersing sodium alginate in water, and then adding an aqueous solution containing a cobalt source, an iron source and thiourea for reaction to obtain SA-CoFe/SNC hydrogel; (b) and (b) freezing and drying the SA-CoFe/SNC hydrogel prepared in the step (a) to obtain an SA-CoFe/SNC aerogel, and then sequentially carrying out primary calcination, acid washing and secondary calcination to obtain the CoFe/SNC composite material. Compared with the prior art, the invention provides a preparation method of a double heteroatom (S, N) co-doped CoFe/SNC composite material capable of being used as a cathode catalyst of a high-efficiency fuel cell, so that the porous honeycomb-shaped CoFe/SNC composite material is obtained, and the catalytic activity, the conductivity, the stability and the methanol tolerance of the catalyst are obviously improved.

Description

Double-heteroatom-doped CoFe/SNC composite material and preparation and application thereof
Technical Field
The invention belongs to the field of material preparation, and particularly relates to a double-heteroatom-doped CoFe/SNC composite material, and preparation and application thereof.
Background
The continued consumption of non-renewable fossil fuels and the increasing desire for global sustainable energy technologies has stimulated the development of new energy technologies such as fuel cells, metal air cells, water splitting, and the like. However, the slow Oxygen Reduction Reaction (ORR) and Oxygen Evolution Reaction (OER) have limited the development of these new energy technologies. The oxygen reduction reaction is a complex multi-electron reaction process including multi-step elementary reactions, at O2During the reduction to water, some intermediates, such as OOH, O and OH, are produced. Therefore, the adsorption capacity of the catalyst to the intermediate is the key to improve the oxygen reduction activity. Although platinum group metal materials (PGM) are still considered to be the most advanced ORR electrocatalytic materials at present, their large-scale application in new energy technologies is limited by factors such as cost, stability, susceptibility to poisoning, and the like. It is clear that the design and development of an economically efficient alternative with high electrocatalytic activity and long-term stability is a crucial factor.
Patent CN107086313B discloses an iron, cobalt and nitrogen co-doped carbon catalyst, a preparation method and application thereof, wherein an iron/cobalt bimetallic zeolite imidazolate framework material is adopted as a precursor, and the iron, cobalt and nitrogen co-doped carbon catalyst is prepared by high-temperature pyrolysis; the iron/cobalt bimetallic zeolite imidazolate framework material is prepared by adopting ferrous sulfate, cobalt nitrate and 2-methylimidazole to carry out self-assembly reaction in a solvent under an oxygen-free environment.
In patent CN107086313B, firstly, the heteroatom in the catalyst is only nitrogen atom, and the present invention is directed to the influence of sulfur and nitrogen double heteroatoms on the performance of the catalyst. Secondly, the specific surface area of the catalyst of the patent (422 m)2Per g) specific surface area of the composite material not according to the invention (1650 m)2The large specific surface area of the present invention is because the pore-rich structure of the hydrogel is maintained by the condensation drying method. Finally, the catalytic performance of the catalyst of this patent is only comparable to commercial Pt/C, whereas the catalytic performance of the composite of the present invention far exceeds commercial Pt/C.
Patent CN111477886A discloses aThe Co-Fe bimetal doped porous carbon-oxygen reduction catalyst comprises the following formula raw materials and components: s doped g-C3N4Polyacrylonitrile, polyvinylpyrrolidine, cobalt-based metal-organic frameworks, K3[Fe(CN)6]. ) In patent CN111477886A, firstly, the preparation of the present invention is simple and the amount of metal used is very small. Secondly, the present invention is directed to the research of the oxygen reduction cathode material itself, and the patent CN111477886A can be derived from the drawings thereof, and focuses on the research of the shell, the baffle plate, etc. of the water bath for chemical reaction.
Disclosure of Invention
The invention aims to provide a double-heteroatom-doped CoFe/SNC composite material and preparation and application thereof, wherein the conductivity of the composite material is improved by co-doping sulfur and nitrogen, and the double active sites are used for catalyzing oxygen reduction together, so that the cost of the composite material is reduced, the defects of easy poisoning, instability and the like of a noble metal catalyst are overcome, and finally, a high-efficiency oxygen reduction catalyst with better stability, methanol tolerance and the like than commercial Pt/C is prepared.
The purpose of the invention is realized by the following technical scheme:
a preparation method of a double-heteroatom-doped CoFe/SNC composite material specifically comprises the following steps:
(a) sodium Alginate (Sodium Alginate, abbreviated as SA) is uniformly dispersed in water, and then an aqueous solution containing a cobalt source, an iron source and thiourea is added (reactants are respectively formed into aqueous solutions to be more beneficial to uniform dispersion of metal) for reaction, so as to obtain the SA-CoFe/SNC hydrogel, wherein the SNC represents a sulfur and nitrogen co-doped carbon carrier, the Sodium Alginate is a metal ion chelating agent, and Sodium ions in Sodium Alginate molecules can perform ion exchange action with polyvalent metal ions, so that the hydrogel is formed, and the Sodium Alginate is beneficial to anchoring of the metal ions.
(b) Freezing and drying the SA-CoFe/SNC hydrogel prepared in the step (a) to obtain a spongy SA-CoFe/SNC aerogel, and then sequentially carrying out primary calcination, acid washing and secondary calcination to obtain the CoFe/SNC composite material. Primary calcination thermally reduces the metal at high temperature and produces an electrically conductive carbon support; the secondary calcination is because the acid washing is performed in the previous step, the acid washing may destroy a carbon structure formed in the previous primary calcination, and the secondary calcination is beneficial to the restoration of the carbon carrier.
In the step (a), the addition ratio of sodium alginate, (cobalt source + iron source) to thiourea is 300mg:0.1mmol (1-2) mmol, preferably 300mg:0.1mmol:2 mmol. In the present invention, the cobalt source and the iron source are regarded as a metal entity, and the sum of both is emphasized in the production, and the molar ratio of the cobalt source to the iron source in the entity may be (0.02-0.08): (0.08-0.02).
In the step (a), cobalt chloride hexahydrate is used as a cobalt source, ferric trichloride is used as an iron source, and the adding amount ratio of sodium alginate to cobalt chloride hexahydrate to ferric trichloride to thiourea is 300mg, (4.8-19) mg, (3.5-13) mg, (1-2) mmol.
In step (a), the volume of the aqueous solution containing sodium alginate is 15-25ml, preferably 20ml, and the water is ultrapure water.
In the step (a), the volume of the aqueous solution containing cobalt chloride hexahydrate, ferric trichloride and thiourea is 15-25ml, preferably 20ml, and the water is ultrapure water.
In the step (a), the reaction temperature is room temperature, the reaction time is 1-2h, and stirring is carried out while the reaction is carried out. During the stirring process, the metal ions of the metal precursor and the sodium ions in the sodium alginate perform ion exchange action, so that a hydrogel-like solution is formed.
In step (b), before freeze-drying, the SA-CoFe/SNC hydrogel is put into a freezing layer at-15 ℃ in a refrigerator for freezing and storing for 12-24h, preferably 24h, so that the hydrogel solution becomes solid. Because the freeze dryer can form negative pressure when carrying out drying work, liquid can be sucked out, and only solid material (or the material that water content is minimum) can put into freeze dryer and carry out freeze-drying.
In step (b), the temperature of freeze-drying is-50 deg.C, the freeze-drying time is 24-48h, preferably 48h, and the vacuum degree is below 20 Pa.
In the step (b), the primary calcination process specifically comprises: heating to 800 ℃ at a heating rate of 3 ℃/min, keeping the temperature for 1-2h, preferably 2h, protecting with inert gas, and grinding after the sample is cooled to room temperature after calcination.
In the step (b), the acid washing process specifically comprises the following steps: acid washing the intermediate product after primary calcination with 0.5M dilute sulfuric acid at 80 deg.C for 8-10h, preferably 10h, suction filtering, and vacuum drying the obtained filter residue at 50-70 deg.C, preferably 60 deg.C for 10-14h, preferably 12 h. The acid wash is to etch away agglomerated metal clusters or unstable metals, thereby allowing the resulting composite to expose more active sites.
In the step (b), the secondary calcination process specifically comprises: heating to 800 ℃ at a heating rate of 3 ℃/min, keeping the temperature for 1-3h, preferably 2h, protecting with inert gas, and grinding after the sample is cooled to room temperature after calcination.
The CoFe/SNC composite material is of a 3D-pore honeycomb structure and has a specific surface area of 1650m2g-1。
Use of a CoFe/SNC composite as described above as a cathode catalyst for a fuel cell.
The invention adopts a carrier doped with sulfur element and nitrogen element as a matrix, and then the cobalt element and the iron element are loaded on the matrix to prepare the composite material. The introduction of the sulfur element causes the defects of the matrix to be increased, the specific surface area is increased, and the specific surface area of the CoFe/SNC composite material which is finally obtained is 1650m2The presence of sulfur accelerates the electron transfer rate and increases the electrical conductivity of the composite material when used as a catalyst. The nitrogen element is introduced to form an active site with cobalt or iron. The CoFe/SNC composite material contains a plurality of active sites, including cobalt-iron alloy and Co-NxAnd Fe-NxThe several active sites together catalyze and promote the oxygen reduction reaction. Wherein, the cobalt-iron alloy can also adjust the surrounding Co-NxAnd Fe-NxThe role of the active site. In addition, the electronegativity of the S element is relatively small, and the electron transfer from the sulfur and nitrogen co-doped graphene structure (namely, the matrix prepared in the step (a)) to the S element can be promotedCo-Nx/Fe-NxSites, increased Co-Nx/Fe-NxThe surrounding electron density. The CoFe/SNC composite material has rich micropores and mesopores and large specific surface area, provides more active sites for oxygen reduction, and is very favorable for contacting with electrolyte and oxygen-containing substances, namely the CoFe/SNC composite material has very excellent ORR activity.
Compared with the prior art, the invention synthesizes hydrogel by a convenient method, and obtains the composite material with a uniform hierarchical porous honeycomb nano structure by calcination.
Drawings
FIG. 1 is a SEM image of a CoFe/SNC composite material prepared in example 1;
FIG. 2 is a TEM image of the CoFe/SNC composite material prepared in example 1;
FIG. 3 is the XRD pattern of the CoFe/SNC catalyst prepared in example 1;
FIG. 4 shows the results of the catalysts of example 1, comparative example 2 and comparative example 3 in O2Linear scan test comparative plot in saturated 0.1m koh solution;
FIG. 5 shows the results of the catalysts of example 1 and comparative example 2 in O2Chronoamperometric comparison plots in saturated 0.1M KOH solutions;
FIG. 6 shows the results of O-catalyzed reactions of the catalysts of example 1 and comparative example 22Comparative plots of methanol tolerance tests in saturated 0.1M KOH solution;
FIG. 7 shows the results of O-catalyzed reactions of catalysts of example 1, comparative example 2, example 2 and example 32Comparison of linear scan tests in saturated 0.1m koh solution.
Detailed Description
The invention is described in detail below with reference to the figures and specific embodiments.
Example 1
A preparation method of a double-heteroatom-doped CoFe/SNC composite material comprises the following steps:
(1) preparation of SA-CoFe/SNC hydrogel.
300mg of sodium alginate is dispersed into 20ml of ultrapure water, and stirred for 1 hour at normal temperature to form a uniform light yellow solution, which is marked as solution A. 19mg of cobalt chloride hexahydrate, 3.5mg of ferric trichloride and 2mmol of thiourea were dispersed in 20ml of ultrapure water (molar ratio of cobalt source to iron source was 4:1), and stirred at room temperature for 1 hour to form a uniform solution, which was denoted as solution B. And pouring the solution B into the solution A, and continuing stirring for 1h to generate the SA-CoFe/SNC hydrogel. And then putting the prepared solution into a freezing layer of a refrigerator, freezing and keeping the temperature at-15 ℃ for 24h, and then freezing and drying the SA-CoFe/SNC hydrogel for 48h under the condition of vacuum degree of-50 ℃ and vacuum degree of below 20 Pa.
(2) Preparation of CoFe/SNC.
The SA-CoFe/SNC hydrogel is frozen and dried to form spongy aerogel, the aerogel is placed in a porcelain boat and is calcined for one time at 800 ℃ for 1h under the Ar inert atmosphere condition, the heating rate is 3 ℃/min, and the vacuum pumping is needed before the tubular furnace is heated. After the sample is naturally cooled to room temperature, the sample is manually ground and collected in a mortar (no requirement on the mesh number, the same below). Followed by dispersion into H at a concentration of 0.5M2SO4Keeping the temperature at 80 ℃ for 10 h. Then vacuum filtering is carried out, a large amount of ultrapure water is used for washing the sample to be neutral, and the sample is put into a vacuum drying oven and dried for 12h at the temperature of 60 ℃. And then carrying out secondary calcination, wherein the calcination temperature is the same as that of the primary calcination, the calcination is carried out for 2h at 800 ℃ in an Ar gas atmosphere, the heating rate is 3 ℃/min, after the sample is naturally cooled to the room temperature, the sample is ground to obtain a CoFe/SNC composite material, the CoFe/SNC composite material is marked as CoFe/SNC-1, and the specific surface area of the CoFe/SNC-1 is 1650m2/g。
The SEM image of the CoFe/SNC-1 scanning electron microscope is shown in figure 1, the TEM image of the transmission electron microscope is shown in figure 2, and it can be seen that the composite material contains a large number of micropores and mesopores, the existence of the micropores increases the specific surface area of the CoFe/SNC catalytic composite material, and the active surface is easily exposed in an electrolyte solution, which is beneficial to accelerating the reaction rate and improving the catalytic activity of the material during the catalytic reaction.
The XRD pattern of the CoFe/SNC-1 is shown in FIG. 3, and from the XRD pattern, the CoFe/SNC composite material has graphite at 22 DEGThe (002) diffraction peak of carbon does not have the crystallization peak of metallic cobalt and metallic iron, which indicates that most Co and Fe elements may exist in the CoFe/SNC composite material in an atomic state. Two diffraction peaks at 43.8 DEG and 51.08 DEG correspond to Co0.72Fe0.28The (330) plane and the (422) plane of the alloy (PDF # 51-0740). The lower peak height of the 51.08 DEG diffraction indicates the poorer crystallinity.
The CoFe/SNC-1 was used as a cathode catalyst (the same applies below) to perform a linear scan test under the following conditions: the initial voltage is 0.19V, the final voltage is 1.19V, the scanning speed is 0.005V/s, the rotating speed is 1600rpm, and O is adopted2Saturated KOH solution (the same applies below) at a concentration of 0.1M, the results are shown in FIGS. 4 and 7, and the half-wave potential (E) of CoFe/SNC-11/2) 0.896V, limiting current density (j)k) Is 5.73mA cm-2。
The CoFe/SNC-1 is subjected to a timing current test under the following test conditions: the initial voltage is 0.84V, the rotating speed is 1600rpm, the running time is 50000s, and O is adopted2Saturated 0.1M KOH solution (same below) resulted in the CoFe/SNC-1 having retained 86.75% current density over 50000s operating conditions as shown in FIG. 5.
The CoFe/SNC-1 is subjected to a methanol tolerance test under the following test conditions: the initial voltage is 0.84V, the rotating speed is 1600rpm, the running time is 5000s, and O is adopted2Saturated 0.1M KOH solution (same below), and the results are shown in FIG. 6, where 3M methanol was added to the 0.1M KOH solution as an electrolyte solution 1000s after the start of the test, CoFe/SNC-1 fluctuated at 1000s, but rapidly stabilized.
Comparative example 1
The Fe/SNC composite material is prepared by the following steps:
(1) preparation of SA-Fe/SNC hydrogel.
300mg of sodium alginate is dispersed into 20ml of ultrapure water, and stirred for 1 hour at normal temperature to form a uniform light yellow solution, which is marked as solution A. 16.2mg of ferric chloride (keeping the total molar amount of metal at 0.1mmol) and 2mmol of thiourea were dispersed in 20ml of ultrapure water and stirred at room temperature for 1h to form a homogeneous solution, denoted as solution B. And pouring the solution B into the solution A, and continuing stirring for 1h to generate the SA-Fe/SNC hydrogel. And then putting the prepared solution into a freezing layer of a refrigerator, freezing and keeping the temperature at-15 ℃ for 24h, and then freezing and drying the SA-Fe/SNC hydrogel for 48h under the conditions of-50 ℃ and the vacuum degree of below 20 Pa.
(2) Preparing Fe/SNC composite material.
The SA-Fe/SNC hydrogel is frozen and dried to form spongy aerogel, the aerogel is placed in a porcelain boat and is calcined for one time at 800 ℃ for 1h under the Ar inert atmosphere condition, the heating rate is 3 ℃/min, and the vacuum pumping is needed before the tubular furnace is heated. And grinding and collecting the sample after the sample is naturally cooled to room temperature. Followed by dispersion into H at a concentration of 0.5M2SO4Keeping the temperature at 80 ℃ for 10 h. Then vacuum filtering is carried out, a large amount of ultrapure water is used for washing the sample to be neutral, and the sample is put into a vacuum drying oven and dried for 12h at the temperature of 60 ℃. And then carrying out secondary calcination, wherein the calcination temperature is the same as that of the primary calcination, the calcination is carried out for 2h at 800 ℃ in the Ar gas atmosphere, the heating rate is 3 ℃/min, and after the sample is naturally cooled to the room temperature, the sample is ground to obtain the Fe/SNC composite material. The results of the linear scan test of the Fe/SNC composite material are shown in FIG. 4, and it can be seen that the half-wave potential (E) of the Fe/SNC composite material1/2) 0.896V, limiting current density (j)k) Is 5.73mA cm-2The half-wave potential and the limiting current density of the Fe/SNC composite material are both smaller than those of the CoFe/SNC-1 prepared in the example 1.
Comparative example 2
A commercial catalyst JM 20% Pt/C from Johnson-Matthery having a specific surface area of 1650m2The catalyst was subjected to a linear scanning test, and the results are shown in FIGS. 4 and 7, and it can be seen that the half-wave potential (E) of the catalyst1/2) 0.862V, limiting current density (j)k) Is 5.26mA cm-2. The catalyst was subjected to chronoamperometric testing and the results are shown in figure 5, which shows that only 44.57% of the current density of commercial Pt/C was retained over 50000s operating conditions. The catalyst was subjected to a methanol tolerance test, and as a result, as shown in FIG. 6, it can be seen that when 3M methanol was added to a 0.1M KOH solution as an electrolyte solution 1000s after the start of the test, there was a significant fluctuation in commercial Pt/C and it could not be achieved even after a considerable time had elapsedThe reason for this is that methanol is electro-oxidized on the commercial Pt/C catalyst, causing the cathode oxygen reduction potential to drop, forming a "mixed potential", so that the performance of the commercial Pt/C catalyst drops sharply.
As can be seen from FIG. 4, the electrical properties of the CoFe/SNC composite material prepared in example 1 are significantly better than those of commercial Pt/C (E)1/2：0.862V；jk：5.26mA cm-2) It can be concluded that the CoFe/SNC catalyst has significantly higher oxygen reduction catalytic activity and conductivity than commercial Pt/C.
As can be seen in FIG. 5, the CoFe/SNC composite has excellent stability over commercial Pt/C.
As can be seen from FIG. 6, the catalytic stability of the CoFe/SNC composite material of the invention in the methanol electro-oxidation process is remarkably improved compared with that of the commercial Pt/C.
Comparative example 3
A Co/SNC composite material is prepared by the following steps:
(1) SA-Co/SNC hydrogels were prepared.
300mg of sodium alginate is dispersed into 20ml of ultrapure water, and stirred for 1 hour at normal temperature to form a uniform light yellow solution, which is marked as solution A. 23.8mg of cobalt chloride hexahydrate (keeping the total molar amount of metals at 0.1mmol) and 2mmol of thiourea were dispersed in 20ml of ultrapure water and stirred at room temperature for 30min to form a homogeneous solution, which was designated as solution B. The solution B is poured into the solution A, and stirring is continued for 1 h. And then putting the prepared solution into a freezing layer of a refrigerator, freezing and keeping the temperature at-15 ℃ for 24 hours, and then freezing and drying the SA-Co/SNC hydrogel for 48 hours under the conditions of-50 ℃ and the vacuum degree of below 20 Pa.
(2) Preparing the Co/SNC composite material.
The SA-Co/SNC is frozen and dried to become light purple aerogel, and the light purple aerogel is put into a porcelain boat and calcined for 1h at 800 ℃ under the inert atmosphere condition, and the heating rate is 3 ℃/min. The tube furnace is evacuated before heating. And grinding and collecting the sample after the sample is naturally cooled to room temperature. Then dispersed to 0.5M H2SO4Keeping the temperature at 80 ℃ for 10 h. Then vacuum filtering is carried out, a large amount of ultrapure water is used for washing the sample to be neutral, and the sample is put into a vacuum drying oven and dried for 12h at the temperature of 60 ℃. Then go intoAnd (3) carrying out secondary calcination, wherein the calcination temperature is the same as that of the primary calcination, the calcination is carried out for 2h at 800 ℃ in the Ar gas atmosphere, the heating rate is 3 ℃/min, and after the sample is naturally cooled to the room temperature, the sample is ground to obtain the Co/SNC composite material. The Co/SNC composite material was subjected to a linear scan test, and the results are shown in FIG. 4, in which it can be seen that the half-wave potential (E) of the Co/SNC composite material1/2) At 0.882V, limiting current density (j)k) Is 5.36mA cm-2The half-wave potential and the limiting current density of the Co/SNC composite material are both smaller than those of the example 1.
As can be seen from FIG. 4, the electrical properties of the CoFe/SNC composite material prepared in example 1 are significantly better than those of the Fe/SNC composite material (E)1/2：0.896V；jk：4.71mAcm-2) Commercial Pt/C (E)1/2：0.862V；jk：5.26mA cm-2) And a Co/SNC composite material, and the CoFe/SNC composite material has high oxygen reduction catalytic activity and conductivity.
In conclusion, the invention is a simple and easy-to-operate method for synthesizing the sulfur and nitrogen co-doped CoFe/SNC composite material, the prepared composite material is a hierarchical porous honeycomb nano structure, and can be used as a cathode catalyst of a fuel cell, and the composite material has excellent electrochemical performance, and has remarkably enhanced cycle stability and methanol tolerance relative to commercial Pt/C.
Example 2
A preparation method of a double-heteroatom-doped CoFe/SNC composite material comprises the following steps:
(1) preparation of SA-CoFe/SNC hydrogel.
300mg of sodium alginate is dispersed into 20ml of ultrapure water, and stirred for 1 hour at normal temperature to form a uniform light yellow solution, which is marked as solution A. 11.9mg of cobalt chloride hexahydrate, 8.1mg of ferric chloride and 2mmol of thiourea were dispersed in 20ml of ultrapure water (molar ratio of cobalt source to iron source is 1:1), and stirred at room temperature for 1 hour to form a uniform solution, which was denoted as solution B. And pouring the solution B into the solution A, and continuing stirring for 1h to generate the SA-CoFe/SNC hydrogel. And then putting the prepared solution into a freezing layer of a refrigerator, freezing and keeping the temperature at-15 ℃ for 24h, and then freezing and drying the SA-CoFe/SNC hydrogel for 48h under the conditions of-50 ℃ and the vacuum degree of below 20 Pa.
(2) Preparation of CoFe/SNC.
The SA-CoFe/SNC hydrogel is frozen and dried to form spongy aerogel, the aerogel is placed in a porcelain boat and is calcined for one time at 800 ℃ for 1h under the Ar inert atmosphere condition, the heating rate is 3 ℃/min, and the vacuum pumping is needed before the tubular furnace is heated. And grinding and collecting the sample after the sample is naturally cooled to room temperature. Followed by dispersion into H at a concentration of 0.5M2SO4Keeping the temperature at 80 ℃ for 10 h. Then vacuum filtering is carried out, a large amount of ultrapure water is used for washing the sample to be neutral, and the sample is put into a vacuum drying oven and dried for 12h at the temperature of 60 ℃. And then carrying out secondary calcination, wherein the calcination temperature is the same as that of the primary calcination, the calcination is carried out for 2h at 800 ℃ in an Ar gas atmosphere, the heating rate is 3 ℃/min, and after the sample is naturally cooled to the room temperature, the sample is ground to obtain the CoFe/SNC composite material, which is marked as CoFe/SNC-2. The results of the linear scan test of this CoFe/SNC-2 are shown in FIG. 7, and it can be seen that the half-wave potential (E) of CoFe/SNC-21/2) 0.892V, limiting Current Density (j)k) Is 5.87mAcm-2Although the limiting current density of CoFe/SNC-2 is greater than that of example 1, the half-wave potential is less than that of example 1, but the half-wave potential is greater than that of the Pt/C catalyst of comparative example 2, which shows that the oxygen reduction capability of CoFe/SNC-2 is slightly weaker than that of CoFe/SNC-1 but better than that of the commercial Pt/C catalyst.
Example 3
A preparation method of a double-heteroatom-doped CoFe/SNC composite material comprises the following steps:
(1) preparation of SA-CoFe/SNC hydrogel.
300mg of sodium alginate is dispersed into 20ml of ultrapure water, and stirred for 1 hour at normal temperature to form a uniform light yellow solution, which is marked as solution A. 4.8mg of cobalt chloride hexahydrate, 13mg of ferric trichloride and 2mmol of thiourea were dispersed in 20ml of ultrapure water (molar ratio of cobalt source to iron source was 1:4), and stirred at room temperature for 1 hour to form a uniform solution, which was denoted as solution B. And pouring the solution B into the solution A, and continuing stirring for 1h to generate the SA-CoFe/SNC hydrogel. And then putting the prepared solution into a freezing layer of a refrigerator, freezing and keeping the temperature at-15 ℃ for 24h, and then freezing and drying the SA-CoFe/SNC hydrogel for 48h under the conditions of-50 ℃ and the vacuum degree of below 20 Pa.
(2) Preparation of CoFe/SNC.
The SA-CoFe/SNC hydrogel is frozen and dried to form spongy aerogel, the aerogel is placed in a porcelain boat and is calcined for one time at 800 ℃ for 1h under the Ar inert atmosphere condition, the heating rate is 3 ℃/min, and the vacuum pumping is needed before the tubular furnace is heated. And grinding and collecting the sample after the sample is naturally cooled to room temperature. Followed by dispersion into H at a concentration of 0.5M2SO4Keeping the temperature at 80 ℃ for 10 h. Then vacuum filtering is carried out, a large amount of ultrapure water is used for washing the sample to be neutral, and the sample is put into a vacuum drying oven and dried for 12h at the temperature of 60 ℃. And then carrying out secondary calcination, wherein the calcination temperature is the same as that of the primary calcination, the calcination is carried out for 2h at 800 ℃ in an Ar gas atmosphere, the heating rate is 3 ℃/min, and after the sample is naturally cooled to the room temperature, the sample is ground to obtain the CoFe/SNC composite material, which is marked as CoFe/SNC-3. The results of the linear scan test of this CoFe/SNC-3 are shown in FIG. 7, and it can be seen that the half-wave potential (E) of CoFe/SNC-31/2) 0.901V, limiting current density (j)k) Is 5.40mAcm-2The limiting current density of CoFe/SNC-3 is less than that of example 1, but greater than that of the Pt/C catalyst of comparative example 2, indicating that the conductivity of CoFe/SNC-3 is slightly less than that of CoFe/SNC-1, but better than that of the commercial Pt/C catalyst.
Example 4
A preparation method of a double-heteroatom-doped CoFe/SNC composite material comprises the following steps: except for the step (1), 1mmol of thiourea is taken, the solution B is poured into the solution A, the stirring is continued for 2 hours, the SA-CoFe/SNC hydrogel is generated, then the prepared solution is put into a refrigerator freezing layer, the temperature is-15 ℃, the freezing is kept for 12 hours, and the SA-CoFe/SNC hydrogel is frozen and dried for 24 hours under the conditions of-50 ℃ and the vacuum degree of below 20 Pa; in the step (2), the primary calcination is carried out for 2h at 800 ℃ under the Ar inert atmosphere condition, the heating rate is 3 ℃/min, the obtained filter residue is dried for 14h in vacuum at 50 ℃, the rest is the same as the example 1 except that the secondary calcination is carried out for 1h at 800 ℃.
Example 5
A preparation method of a double-heteroatom-doped CoFe/SNC composite material comprises the following steps: except for the step (1), 1mmol of thiourea is taken, the solution B is poured into the solution A, the stirring is continued for 2 hours, the SA-CoFe/SNC hydrogel is generated, then the prepared solution is put into a refrigerator freezing layer, the temperature is-15 ℃, the freezing is kept for 16 hours, and the SA-CoFe/SNC hydrogel is frozen and dried for 28 hours under the conditions of-50 ℃ and the vacuum degree of below 20 Pa; in the step (2), the primary calcination is carried out for 1.5h at 800 ℃ under the Ar inert atmosphere condition, the heating rate is 3 ℃/min, the obtained filter residue is dried for 10h in vacuum at 70 ℃, the secondary calcination is carried out for 3h at 800 ℃, and the rest is the same as the example 1.
The embodiments described above are described to facilitate an understanding and use of the invention by those skilled in the art. It will be readily apparent to those skilled in the art that various modifications to these embodiments may be made, and the generic principles described herein may be applied to other embodiments without the use of the inventive faculty. Therefore, the present invention is not limited to the above embodiments, and those skilled in the art should make improvements and modifications within the scope of the present invention based on the disclosure of the present invention.

Claims (10)

1. The preparation method of the double-heteroatom-doped CoFe/SNC composite material is characterized by comprising the following steps of:
(a) uniformly dispersing sodium alginate in water, and then adding an aqueous solution containing a cobalt source, an iron source and thiourea for reaction to obtain SA-CoFe/SNC hydrogel;
(b) and (b) freezing and drying the SA-CoFe/SNC hydrogel prepared in the step (a) to obtain an SA-CoFe/SNC aerogel, and then sequentially carrying out primary calcination, acid washing and secondary calcination to obtain the CoFe/SNC composite material.
2. The method for preparing the double-heteroatom-doped CoFe/SNC composite material as claimed in claim 1, wherein in the step (a), the cobalt source is cobalt chloride hexahydrate, and the iron source is ferric trichloride.
3. The preparation method of the double-heteroatom-doped CoFe/SNC composite material as claimed in claim 1, wherein in the step (a), the addition ratio of sodium alginate, a cobalt source and an iron source to thiourea is 300mg:0.1mmol (1-2) mmol.
4. The method for preparing the double-heteroatom-doped CoFe/SNC composite material according to claim 1, wherein in the step (a), the reaction temperature is room temperature, the reaction time is 1-2h, and stirring is carried out while the reaction is carried out.
5. The method for preparing the double-heteroatom-doped CoFe/SNC composite material according to claim 1, wherein in the step (b), the temperature of freeze drying is-50 ℃, and the time of freeze drying is 24-48 h.
6. The method for preparing the double-heteroatom-doped CoFe/SNC composite material according to claim 1, wherein in the step (b), a calcination process specifically comprises the following steps: heating to 800 ℃ at the heating rate of 3 ℃/min, keeping the temperature for 1-2h, protecting by using inert gas, and grinding after the sample is cooled to room temperature after calcination is finished.
7. The method for preparing the double-heteroatom-doped CoFe/SNC composite material according to claim 1, wherein in the step (b), the acid washing process specifically comprises the following steps: acid washing the intermediate product after primary calcination with 0.5M dilute sulfuric acid at 80 deg.C for 8-10h, vacuum filtering, and vacuum drying the obtained filter residue at 50-70 deg.C for 10-14 h.
8. The method for preparing the double-heteroatom-doped CoFe/SNC composite material according to claim 1, wherein in the step (b), the secondary calcination process specifically comprises the following steps: heating to 800 ℃ at the heating rate of 3 ℃/min, keeping the temperature for 1-3h, protecting by using inert gas, and grinding after the sample is cooled to room temperature after calcination is finished.
9. A dual heteroatom doped CoFe/SNC composite material prepared by the preparation method according to any one of claims 1 to 8, wherein the CoFe/SNC composite material is a 3D graded porous honeycomb structure.
10. Use of the CoFe/SNC composite material according to claim 9 as a cathode catalyst for a fuel cell.
CN202110431056.2A 2021-04-21 2021-04-21 Double-heteroatom-doped CoFe/SNC composite material and preparation and application thereof Pending CN113285079A (en)

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