CN113871642B - Nitrogen-doped carbon-loaded Mo/Pt alloy catalyst and application thereof - Google Patents

Nitrogen-doped carbon-loaded Mo/Pt alloy catalyst and application thereof Download PDF

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CN113871642B
CN113871642B CN202110969948.8A CN202110969948A CN113871642B CN 113871642 B CN113871642 B CN 113871642B CN 202110969948 A CN202110969948 A CN 202110969948A CN 113871642 B CN113871642 B CN 113871642B
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nitrogen
doped carbon
polypyrrole
alloy catalyst
supported
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CN113871642A (en
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陈伟
唐文静
杨圣双
施妙艳
岑朝杰
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Wenzhou 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
    • H01M4/92—Metals of platinum group
    • H01M4/921—Alloys or mixtures with metallic elements
    • 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
    • H01M4/92—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

Abstract

The invention belongs to the technical field of electrochemical catalyst materials, and particularly relates to a nitrogen-doped carbon-supported Mo/Pt alloy catalyst and application thereof. The nitrogen-doped carbon-loaded Mo/Pt alloy catalyst is prepared by directly carrying out solid-phase heat treatment after mixing raw materials, and the process is simple. The catalyst has high activity, stability and methanol poisoning resistance to oxygen reduction reaction.

Description

Nitrogen-doped carbon-loaded Mo/Pt alloy catalyst and application thereof
Technical Field
The invention belongs to the technical field of electrochemical catalyst materials, and particularly relates to a nitrogen-doped carbon-supported Mo/Pt alloy catalyst and application thereof.
Background
The development of science and technology tends to increase the energy demand, especially the consumption of fossil fuels, which are non-renewable energy sources, which has forced people to search and produce ecologically friendly materials to replace non-renewable fuels. Currently, fuel cells are receiving extensive attention for their advantages of high energy conversion efficiency, low pollutant emission, etc., and the cathodic oxygen reduction (ORR) reaction is a critical step. However, there are still problems to be solved in the oxygen reduction reaction process, such as: the reaction kinetics is slower, and the ideal effect is not achieved; pt can promote the efficient progress of the oxygen reduction reaction, but its long-term cycle stability and poison resistance have a large room for improvement; pt is also economically unfriendly and accounts for approximately 20% of the cost of fuel cells. The commercial application of fuel cells is greatly limited by the problems of the Pt catalyst such as unfriendly economy, poor stability, weak poisoning resistance, and improved reaction kinetics. In summary, it is imperative to develop a fuel cell cathode catalyst with high catalytic activity, long-term use stability, strong poisoning resistance and low cost. The alloy formed by cheaper metals and noble metals is an effective way, on one hand, the addition of another metal can effectively reduce the consumption of noble metals, and on the other hand, the interaction between the two metals is expected to improve the catalytic performance and stability. However, the formation of the alloy often requires higher temperatures, the liquid phase reaction is suitable for the synthesis of only a small portion of the alloy, and the surfactant is required to stabilize the product against agglomeration, and the final residual surfactant can seriously affect the activity and stability of the catalyst.
Disclosure of Invention
The invention aims to overcome the defects and the shortcomings of the prior art and provide a nitrogen-doped carbon-loaded Mo/Pt alloy catalyst and application thereof.
The technical scheme adopted by the invention is as follows: the preparation method of the nitrogen-doped carbon-supported Mo/Pt alloy catalyst comprises the following steps:
(1) Preparation of nanospheres polypyrrole: adding propionic acid into a container, heating to 130-160 ℃, mixing pyrrole with propionic acid to obtain pyrrole propionic acid solution, adding the pyrrole propionic acid solution into propionic acid in the container heated to 130-160 ℃ under stirring, and reacting for at least 1.5h by using oxygen as an oxidant to obtain black mixed solution; washing and separating the product with ethanol and water, and finally drying to obtain nano spherical polypyrrole;
(2) Preparation of a nitrogen-doped carbon-supported Mo/Pt alloy catalyst: and (3) dipping molybdate and chloroplatinic acid into the pore canal of the nano spherical polypyrrole prepared in the step (1), and calcining to obtain the nitrogen-doped carbon-loaded Mo/Pt alloy catalyst.
In some embodiments of the invention, in step (1), the pyrrole propionic acid solution is slowly added to propionic acid in a vessel heated to 130-160 ℃ and the step is added for 0-15min, preferably for 5-10 min.
In some embodiments of the invention, in step (1), the stirring speed is from 450 to 550 rpm.
In some embodiments of the invention, in step (1), the reaction time is 180 minutes.
In some embodiments of the invention, in step (1), the ratio of the total volume of propionic acid to the mass of pyrrole is 15:19-57, with a ratio of total volume of propionic acid to mass of pyrrole of 15:57 being most preferred.
In some embodiments of the present invention, in step (2), the nano-spherical polypyrrole prepared in step (1) is dispersed in water, then glacial acetic acid is added into the polypyrrole dispersion liquid, molybdate and palladium salt are added, stirring and impregnation are performed, so that the molybdate and palladium salt are impregnated into pore channels of the nano-spherical polypyrrole, and calcination is performed after drying treatment.
In some embodiments of the invention, hydrogen is used as a reducing atmosphere and argon is used as a protective atmosphere during calcination.
In some embodiments of the invention, the calcination temperature is 670-820 ℃, with 770 ℃ being most preferred.
In some embodiments of the invention, the calcination time is 10-60 minutes, with 30 minutes being most preferred.
In some embodiments of the invention, the total metal loading is 1-6mg/25mg polypyrrole, with 4 mg/25mg polypyrrole being most preferred.
In some embodiments of the invention, the molar ratio of Mo to Pt is 2-1:1-3, with a molar ratio of Mo to Pt of 2:3 being most preferred.
The use of a nitrogen-doped carbon-supported Mo/Pt alloy catalyst as described above as a redox electrocatalyst.
A fuel cell wherein the catalyst is a nitrogen doped carbon supported Mo/Pt alloy catalyst as described above.
The beneficial effects of the invention are as follows: the nitrogen-doped carbon-loaded Mo/Pt alloy catalyst is prepared by directly carrying out solid-phase heat treatment after mixing raw materials, and the process is simple. The catalyst has high activity, stability and methanol poisoning resistance to oxygen reduction reaction.
Drawings
In order to more clearly illustrate the embodiments of the invention or the technical solutions of the prior art, the drawings which are required in the description of the embodiments or the prior art will be briefly described, it being obvious that the drawings in the description below are only some embodiments of the invention, and that it is within the scope of the invention to one skilled in the art to obtain other drawings from these drawings without inventive faculty.
FIG. 1 is a scanning electron micrograph of polypyrrole prepared at various feed times: (a) 0 min; (b) 5min; (c) 10 min; (d) 15min;
FIG. 2 is a scanning electron micrograph of polypyrrole prepared at various stirring speeds (a) 300 rpm; (b) 400 rpm; (c) 500 rpm; (d) 600 rpm;
FIG. 3 is a scanning electron micrograph of polypyrrole prepared at various feed ratios, the amount of pyrrole (a) 190 mg; (b) 380 mg; (c) 570 mg; (d) 760 mg;
FIG. 4 is a scanning electron micrograph of polypyrrole prepared in comparative example 1;
FIG. 5 is Mo 0.29 Pt 0.71 SEM image of/N-C, (a), TEM image (b), high resolution transmission electron microscope image (C), and (d) is a white box magnified region of image (C);
FIG. 6 is Mo 0.29 Pt 0.71 N-C high-angle annular dark field transmission electron microscope pictures (a), pt, mo, C, N element signal superposition pictures (b), mo element distribution (C) and Pt element distribution (d);
FIG. 7 is Mo 0.29 Pt 0.71 Nitrogen adsorption-desorption isotherm (a) for N-C, pore size distribution map (b);
FIG. 8 shows PPY, mo 0.29 Pt 0.71 ORR polarization curve of the catalyst (a), tafel slope (b), of the catalyst/N-C, pt/C (20%), mo/N-C, pt/N-C; mo (Mo) 0.29 Pt 0.71 Active area (C), kinetic current density (d), mass specific activity (e), area specific activity (f) of N-C and Pt/C (20%);
in FIG. 9, (a) Mo 0.29 Pt 0.71 N-C cycle stability test; (b) Mo (Mo) 0.29 Pt 0.71 Comparison of anti-methanol poisoning ability of N-C, pt/C (20%);
FIG. 10 is a scanning electron micrograph of a MoPt/N-C catalyst prepared at various reaction temperatures: (a) 670 ℃; (b) 720 ℃; (c) 770 ℃; (d) 820 ℃;
FIG. 11 is an ORR polarization curve of MoPt/N-C prepared at different reaction temperatures;
FIG. 12 is a scanning electron micrograph of MoPt/N-C samples prepared at various reaction times: (a) 10 min; (b) 20 min; (c) 30 min; (d) 40 min; (e) 50 min; (f) 60 min;
FIG. 13 is an ORR polarization curve of MoPt/N-C prepared at different reaction times;
FIG. 14 is a scanning electron micrograph of MoPt/N-C prepared at various loadings: (a) 1 mg; (b) 2 mg; (c) 3 mg; (d) 4 mg; (e) 5 mg; (f) 6 mg;
FIG. 15 is an ORR polarization curve for MoPt/N-C preparation at various loadings;
FIG. 16 is a scanning electron micrograph of MoPt/N-C prepared at various molar ratios (Mo/Pt): (a) 2/1; (b) 1/1; (c) 2/3; (d) 1/2; (e) 1/2.5; (f) 1/3;
FIG. 17 shows ORR polarization curves of MoPt/N-C prepared with different molar ratios (1/2, 1/1, 3/2, 2/1, 5/2, 6/2, respectively).
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings, for the purpose of making the objects, technical solutions and advantages of the present invention more apparent.
Example 1:
105 mL propionic acid was placed in a round bottom flask, a magnet was added, the rotation speed was set at 500rpm, and the temperature was raised to 145 ℃. Weighing 190 mg pyrrole solution by an electronic balance, dissolving in 45 mL propionic acid, dripping into a round bottom flask for about 10min, reacting 3 h, and washing with ethanol and water after the reaction to obtain solid black powder, namely the nano spherical polypyrrole.
Examples 2 to 4
The addition time of the pyrrole solution in example 1 was changed to 0, 5 and 15min respectively, and the morphology of the obtained product was shown in fig. 1.
The morphology of polypyrrole prepared at different feeding times is studied, as shown in fig. 1 (a), pyrrole is directly added into propionic acid under the condition of 0min, and the polypyrrole is in a spherical structure as a whole, but a small part of polypyrrole has non-spherical irregular shapes; when the feeding time is slowed down to 5min, as shown in fig. 1 (b), the product is composed of balls, has uniform size, is distributed at about 250nm, and shows excellent dispersibility; when the feeding time is slowed down to 10min, as shown in fig. 1 (c), the uniformity and the dispersity of the product size distribution are still good, and the yield is more than 2 times of that obtained under the condition of 5min feeding time; when the charging time was 15min, as shown in FIG. 1 (d), the product size started to become uneven. In summary, the preferable feeding time is 5-10min, and the optimal feeding time is 10min.
Examples 5 to 7:
the stirring speeds in example 1 were changed to 300, 400 and 600 rpm, respectively, to obtain the product morphology as shown in FIG. 2.
The appearance of polypyrrole prepared at different stirring speeds is studied, and as shown in fig. 2 (a), under the condition of 300 rpm, the prepared polypyrrole is uneven in size, has other irregular shapes, but most of the polypyrrole maintains a spherical structure; when the stirring speed was increased to 400 rpm, as shown in FIG. 2 (b), the spherical structure was more and more uniform, and the dispersibility was improved; when the stirring speed is increased to 500rpm, as shown in fig. 2 (c), the irregular shape completely disappears, the product is polypyrrole nanospheres, the size distribution is narrow, and the dispersibility is good; when the stirring speed was increased to 600 rpm, as shown in FIG. 2 (d), the product exhibited a broad size distribution and some degree of blocking occurred. In summary, the optimal stirring speed was 500 rpm.
Examples 8 to 10:
the quality of pyrrole in example 1 was changed to 190, 380, 760 and mg respectively, and the morphology of the obtained product was as shown in fig. 3.
The morphology of the polypyrrole prepared by different feeding ratios is studied, and as shown in the figure 3 (a), the size distribution of the prepared polypyrrole is narrower under the condition that the ratio of the total volume of propionic acid to the mass of pyrrole is 15:19, and only slight adhesion occurs, but the yield is lower; under the condition that the ratio of the total volume of propionic acid to the mass of pyrrole is 15:38, as shown in fig. 3 (b), the appearance of the product is still in a spherical structure, but compared with (a), the product has relatively wide size distribution, partial spheres are adhered to form cucurbit polypyrrole, and the yield is low; when the ratio of the total volume of propionic acid to the mass of pyrrole is 15:57, as shown in fig. 3 (c), the size distribution and the dispersibility are good, and the yield is high; when the ratio of total propionic acid volume to pyrrole mass was 15:76, as shown in FIG. 3 (d), extremely uneven and severe blocking of nanosphere size occurred. In summary, the optimal feed ratio is that the ratio of the total volume of propionic acid to the mass of pyrrole is 15:57, and the ratio of the total volume of propionic acid to the mass of pyrrole is 15:57.
Comparative example 1:
placing 150 mL propionic acid and 190 mg pyrrole solution into a round bottom flask, adding magneton, heating to 145 ℃, reacting for 180min, and washing with ethanol and water after the reaction is finished to obtain solid black powder.
As shown in FIG. 4, the reaction gave spherical polypyrrole, but polypyrrole exhibited a broad adhesion and size distribution, and other irregular shapes occurred.
Example 11:
(1) The polypyrrole of 25mg was accurately weighed with an electronic balance and placed in a 20mL beaker, 15 mL water was added and stirring was continued until the polypyrrole was well dispersed in the water. Then placing the dispersed polypyrrole solution into an ultrasonic machine for ultrasonic treatment, adding 0.2 mL glacial acetic acid, uniformly mixing, and adding ammonium molybdate ((NH) 4 ) 6 Mo 7 O 24 ·4H 2 O) and finally chloroplatinic acid (total amount of the two metals 4mgThe mole ratio of Mo to Pt is 2/3), continue to ultrasonic, stir and impregnate 12 h, oven dry.
(2) The dried sample was placed in a quartz boat and heat treated at a set temperature using a tube furnace at 95% Ar and 5% H 2 And (3) respectively carrying out air exhaust for 30min to remove air in the equipment, and heating to 670 ℃ and preserving heat for 30min after the air exhaust is finished. After the reaction is finished, cooling to room temperature, and taking out the sample to obtain the MoPt/N-C catalyst.
Using Inductively Coupled Plasma (ICP) testing and calculation: the molar ratio of Mo to Pt in the sample prepared in this example was 1/2.5, and the MoPt/N-C catalyst prepared in this example was prepared from Mo 0.29 Pt 0.71 N-C.
Comparative example 2:
(1) The polypyrrole of 25mg was accurately weighed with an electronic balance and placed in a 20mL beaker, 15 mL water was added and stirring was continued until the polypyrrole was well dispersed in the water. Then placing the dispersed polypyrrole solution into an ultrasonic machine for ultrasonic treatment, adding 0.2 mL glacial acetic acid, uniformly mixing, and adding ammonium molybdate ((NH) 4 ) 6 Mo 7 O 24 ·4H 2 O) (total amount of Mo 4 mg), continuing to ultrasonic, stirring and impregnating 12 h, and drying.
(2) The dried sample was placed in a quartz boat and heat treated at a set temperature using a tube furnace at 95% Ar and 5% H 2 And (3) respectively carrying out air exhaust for 30min to remove air in the equipment, and heating to 670 ℃ and preserving heat for 30min after the air exhaust is finished. After the reaction is finished, cooling to room temperature, and taking out the sample to obtain the Mot/N-C catalyst.
Comparative example 3:
(1) The polypyrrole of 25mg was accurately weighed with an electronic balance and placed in a 20mL beaker, 15 mL water was added and stirring was continued until the polypyrrole was well dispersed in the water. Then placing the dispersed polypyrrole solution into an ultrasonic machine for ultrasonic treatment, adding 0.2 mL glacial acetic acid, uniformly mixing, adding chloroplatinic acid (the total amount of platinum is 4 mg), continuing ultrasonic treatment, stirring, dipping 12 h, and drying.
(2) The dried sample was placed in a quartz boat and heat treated at a set temperature using a tube furnace at 95% Ar and 5% H 2 And (3) respectively carrying out air exhaust for 30min to remove air in the equipment, and heating to 670 ℃ and preserving heat for 30min after the air exhaust is finished. After the reaction, cooling to room temperature, taking out the sample to obtain the Pt/N-C catalyst.
Comparative example 4:
and filling polypyrrole of 25mg into a quartz boat, and preserving heat at 720 ℃ for 2 h to obtain the N-C catalyst.
FIG. 5 (a) shows Mo 0.29 Pt 0.71 SEM image of N-C sample, and (b) transmission electron microscope image. The observation of both (a) and (b) shows that the N-C material maintains a spherical structure after high temperature annealing, and that the metal nanoparticles are obviously supported in the nitrogen-carbon material, and that FIG. 5 (C) is Mo 0.29 Pt 0.71 The high-resolution transmission electron microscope image of/N-C can be seen, the size of the metal nano particles can be seen to be below 10 nm, and the side surface shows that the carbon-nitrogen material has an extremely important role in limiting the size of the metal particles. (d) The graph is a white box enlargement of the graph (c), the lattice fringe related information is given in the graph (d), the lattice fringe related information is given in the graph, the lattice distance of 0.22 nm corresponds to the (111) plane of the Mo-Pt alloy, which indicates that the successful synthesis of the Mo-Pt alloy phase, the lattice distance of 0.21 nm can be attributed to the fact that after Mo element is introduced into the catalyst, the lattice distance of Pt is obviously compressed from 0.221 nm to 0.21 nm of the pure Pt (111) plane, so that the adsorption energy between the catalyst and oxygen can be changed, which may be one of the reasons why the catalyst performance is superior to that of pure Pt. As shown in FIG. 6, for Mo 0.29 Pt 0.71 The N-C sample was subjected to an elemental species distribution test, and (a) and (b) showed that the sample contained four elements of platinum (Pt), molybdenum (Mo), nitrogen (N), and carbon (C), consistent with the results of elemental analysis. (c) And (d) further prove that the catalyst contains platinum (Pt) and molybdenum (Mo) elements.
And adopting a physical adsorption device nitrogen adsorption and desorption device to acquire data. FIG. 7 shows the catalyst Mo 0.29 Pt 0.71 N-C nitrogen adsorption-desorption isothermal curve (a) and pore size distribution research (b) thereof, wherein in the isothermal curve composed of the two, a relatively obvious hysteresis loop serving as a mesoporous material mark is provided, which indicates that the prepared Mo 0.29 Pt 0.71 The N-C catalyst is mesoporous material, and then the total adsorption quantity of the target catalyst is 164.5 cm through the adsorption-desorption curve 3 g -1 . To further prove poly Mo 0.29 Pt 0.71 N-C is mesoporous material, and Mo can be seen by performing pore size distribution test (b) on the mesoporous material 0.29 Pt 0.71 The pore size distribution of the N-C catalytic material is more concentrated than that of the nitrogen-carbon material obtained after high-temperature calcination, and is mainly 3.72 nm, probably because the MoPt size formed after calcination is more uniform, and the swelling degree of the carbon matrix is basically consistent. To sum up, mo 0.29 Pt 0.71 The N-C material is a mesoporous material, on one hand, active sites can be provided as much as possible in the catalytic process of the oxygen reduction reaction, and on the other hand, proper mesopores can also provide convenience for the transmission of oxygen, so that the oxygen reduction reaction can be performed efficiently.
FIG. 8 is a schematic diagram of PPY, pt/C (20%), mo/N-C, pt/N-C, mo 0.29 Pt 0.71 LSV curves of N-C etc. catalysts. The analyzed LSV curve gives: first, the initial potentials, PPY, pt/C (20%), mo/N-C, pt/N-C, mo0.29Pt0.71/N-C correspond to 0.72V (vs. RHE), 0.975V (vs. RHE), 0.87V (vs. RHE), 0.985V (vs. RHE), 1.06V (vs. RHE), the closest to the theoretical value of 1.23V being Mo 0.29 Pt 0.71 N-C catalyst, sufficient to illustrate Mo 0.29 Pt 0.71 excellent/N-C. The half-wave potential value was 0.970V (Mo 0.29 Pt 0.71 N-C), 0.87V (Pt/N-C), 0.869V (Pt/C (20%)), 0.743V (Mo/N-C), and 0.581V (PPY) are all compared with the reversible hydrogen electrode to find the target catalyst Mo 0.29 Pt 0.71 The half-wave potential of the catalyst/N-C is far higher than that of Pt/C (20%) 100 mV, and the target catalyst is fully proved to have better catalytic performance. For limiting current, it can be seen that Mo 0.29 Pt 0.71 /NThe C catalyst is significantly higher than other catalysts except Pt/C (20%), thus demonstrating that the mass transfer process is superior to other similar reference catalysts. (b) The Tafil slope of the plot was 59 mV dec -1 （Mo 0.29 Pt 0.71 /N-C）、70 mV dec -1 （Pt/C（20%））、81 mV dec -1 （Pt/N-C）、88 mV dec -1 （Mo/N-C）、119 mV dec -1 (N-C), further indicating that the target catalysis gives the fastest reaction kinetics. FIG. (c) is a graph obtained by cyclic voltammetry in an electrolyte solution in which inert gas is always saturated, mo 0.29 Pt 0.71 The more desirable ECSA of N-C demonstrates that it can supply more active sites for the oxygen reduction process to ensure high quality progress of the reaction. As clearly shown in the histogram of the graph (d), mo 0.29 Pt 0.71 Comparison of N-C with Pt/C (20%), mo at each potential 0.29 Pt 0.71 The current densities of the/N-C kinetic control are all the most competitive. For materials containing noble metals, mass specific activity (MA) and area Specific Activity (SA) are also one of the important criteria for measuring the quality of catalyst materials. The bar graphs of FIGS. (e) and (f) clearly show Mo at different overpotential 0.29 Pt 0.71 Both MA and SA of the N-C catalyst are better than Pt/C (20%). Taking 0.9. 0.9V as an example, mo 0.29 Pt 0.71 The mass specific activity of N-C was 9.5 times that of Pt/C (20%), and the area specific activity was about 4.6 times that of Pt/C (20%). Fully proves Mo 0.29 Pt 0.71 The N-C catalyst has more practical value than Pt/C (20%).
The catalyst keeps long-term operation activity, and is the basis of long-term use value of the material. The sample was subjected to stability testing by cyclic voltammetry, which was performed in a mixed kinetic and diffusion controlled zone. As shown in FIG. 9 (a), mo 0.29 Pt 0.71 Polarization curves of the N-C catalyst before and after 5000 circles of test can be well overlapped, which proves that the material can keep good stability. Methanol fuel cells are one type of fuel cell, and resistance to methanol poisoning is particularly important in such fuel cells, such asFIG. 9 (b) shows a corresponding test, when the reaction proceeds to 300 s, 1M CH is added 3 The current of Pt/C (20%) was found to decay rapidly after addition of the OH solution, eventually to 47.55%, in contrast to Mo 0.29 Pt 0.71 The N-C catalyst had a slight deterioration at a moment, but the activity was slightly recovered after the deterioration, and finally, the deterioration was 3.9%, indicating that Mo 0.29 Pt 0.71 N-C has excellent methanol poisoning resistance.
Examples 12 to 14:
the holding temperatures at 720℃in the step (2) in example 11 were changed to 670, 720 and 820℃respectively.
The morphology of the obtained product is shown in fig. 10, and in the whole, after high-temperature annealing, the spherical structure is not collapsed, the structure of the precursor is still well maintained, the obtained sample is almost consistent with the morphology of the N-C material when the temperature is 670 ℃ as shown in fig. (a), and no metal nano particles are found on the outer surface of the N-C material. At 720C, as in graph (b), it was found that the sample was still substantially consistent with the morphology of the N-C material, but careful observation showed that there were many small metal nanoparticles on the nanosphere surface that could not break the carbon layer due to insufficient temperature. When the temperature reaches 770 ℃, as shown in a graph (c), the surface of the nanosphere can be clearly seen to be very rough, a large number of tiny metal particles are loaded on the nanosphere, the sesame-like spherical structure can reveal more active sites, and the relatively open structure also provides convenience for continuous transmission of oxygen molecules.
As shown in FIG. 11, polarization curves of MoPt/N-C catalysts were obtained at different temperatures. The important electrochemical parameters for distinguishing the oxidation-reduction reaction performance are limiting current density and half-wave potential, and compared with the test performance of samples prepared at other temperatures, the LSV curve obtained by testing the samples at 770 ℃ has the maximum limiting current density and the maximum half-wave potential.
From the analysis, 770℃was confirmed as the optimal reaction temperature.
Examples 15 to 19:
the 30min incubation time of step (2) in example 11 was changed to 10min, 20min, 40min, 50min, 60min, respectively, to obtain the product morphology as shown in fig. 12.
FIGS. 12 (a) - (e) are SEM images of MoPt/N-C prepared at different reaction times (10 min, 20min, 30min, 40min, 50min, 60 min). And (3) a sample. The samples in the diagrams (a) and (b) have a certain difference from the surface morphology of the long-time annealed sample (more than 30 min) due to the shorter annealing time, and the etching degree of the N-C material by metal is insufficient, because the surfaces of the nitrogen-carbon materials in the diagrams (a) and (b) are not rough enough, and the relatively closed state is unfavorable for the transmission of protons and reactants in the oxygen reduction reaction process. However, in the samples prepared under the annealing conditions of (e) 50min and (f) 60min, a portion of the n—c was etched away by the metal, leaving the agglomerated metal nanoparticles exposed, and in the ORR reaction (fig. 13), the metal nanoparticles were very coated with the reactants and the hydroxide present in the solution, resulting in that the reactivity was also affected. When the annealing temperature is 30min, the surface of the N-C nanosphere forms a rough structure, and the metal particles are uniformly dispersed on the surface of the N-C nanosphere, so that better catalytic activity can be achieved. The performance of MoPt/N-C samples prepared under different reaction time conditions was characterized by Linear Sweep Voltammetry (LSV). 30 The half-wave potential of the prepared sample is the most positive in min, and the absolute value of the limiting current density is the most positive, so that the optimal oxygen reduction is proved when the reaction time is 30min.
Examples 20 to 24:
the total amount of Mo and Pt in the step (1) in the example 11 is changed to 1mg, 2mg, 3mg, 5mg and 6mg respectively, and the morphology of the obtained product is shown in FIG. 14.
Fig. 14 (a) - (f) are electron microscope images of samples prepared at total metal loadings of 1mg, 2mg, 3mg, 4mg, 5mg, 6 mg. As shown in fig. (a), (b) and (C), the surface morphology of the sample photographed by SEM is almost identical to that of polypyrrole, which may be due to the fact that the amount of metal in the polypyrrole pores is too small, and the polypyrrole has sufficient confinement ability to encapsulate the metal particles in the pores after high temperature annealing, and furthermore, it was found that a small amount of metal nanoparticles exist outside the N-C material because a small amount of metal salt does not remain outside the polypyrrole during the impregnation process, and clusters together to form large-sized nanoparticles during high temperature annealing. When the metal loading is slightly high, the metal particles gathered on the outer layer of the polypyrrole can nucleate at high temperature, have the capability of bursting the cladding of the polypyrrole to a certain extent, cause the rough surface state of the polypyrrole, form more active sites, and improve the contact between oxygen and the active sites, thereby improving the activity of oxidation-reduction reaction.
In order to verify the relationship between the morphology structure of the sample and the catalytic performance of the oxygen reduction reaction, performance tests are carried out on samples with different loading amounts (figure 15), and by combining corresponding scanning electron microscope images, it can be seen that 1mg of the sample with 2mg is relatively compact due to polypyrrole coating, the limiting current density of the oxygen reduction reaction is at a lower level, and when the loading amount is relatively high, the surface of the polypyrrole becomes rough and exposes more metal active sites, and the limiting current is increased. When the total metal load is 4mg, the half-wave potential is most positive. Therefore, the experimental result analysis shows that the performance is optimal when the load amount is 4 mg.
Examples 25 to 29:
the molar ratios of Mo to Pt in step (1) of example 11 were changed to 2/1, 1/2, 1/2.5, 1/3, respectively, to give the product morphology as shown in FIG. 16.
FIGS. 16 (a) - (e) are SEM images of MoPt/N-C catalysts prepared when the molar ratio of the two metals Mo and Pt was 2/1, 1/1, 2/3, 1/2, 1/2.5, 1/3. Since the total load of metals is the same, the samples prepared under different conditions are not greatly different from each other when observed from an electron microscope, and the spherical structure of polypyrrole is maintained, except that the surface of polypyrrole becomes rough when the load of Pt is increased. FIG. 17 shows polarization curves of oxygen reduction reactions for preparing MoPt/N-C under different metal molar ratios, and it can be seen from the curves that when the mole ratio of metal Mo and Pt is greater than 1, the difference of the electrocatalytic oxygen reduction reaction performance is not very large, and when the mole ratio is 3/2, half-wave potential is dominant, namely, the optimal metal mole ratio is Mo/Pt is 2/3.
The foregoing disclosure is illustrative of the present invention and is not to be construed as limiting the scope of the invention, which is defined by the appended claims.

Claims (9)

1. The nitrogen-doped carbon-loaded Mo/Pt alloy catalyst is characterized by comprising the following steps of:
(1) Preparation of nanospheres polypyrrole: adding propionic acid into a container, heating to 130-160 ℃, mixing pyrrole with propionic acid to obtain pyrrole propionic acid solution, adding the pyrrole propionic acid solution into propionic acid in the container heated to 130-160 ℃ under stirring, and reacting for at least 1.5h by using oxygen as an oxidant to obtain black mixed solution; washing and separating the product with ethanol and water, and finally drying to obtain nano spherical polypyrrole;
(2) Preparation of a nitrogen-doped carbon-supported Mo/Pt alloy catalyst: and (3) dipping molybdate and chloroplatinic acid into the pore canal of the nano spherical polypyrrole prepared in the step (1), and calcining to obtain the nitrogen-doped carbon-loaded Mo/Pt alloy catalyst.
2. The nitrogen-doped carbon-supported Mo/Pt alloy catalyst according to claim 1, wherein: in the step (2), the nano spherical polypyrrole prepared in the step (1) is dispersed in water, glacial acetic acid is added into the polypyrrole dispersion liquid, molybdate and palladium salt are added, stirring and dipping are carried out, so that the molybdate and the palladium salt are dipped into pore channels of the nano spherical polypyrrole, and the nano spherical polypyrrole is calcined after drying treatment.
3. The nitrogen-doped carbon-supported Mo/Pt alloy catalyst according to claim 1, wherein: during calcination, hydrogen is used as a reducing atmosphere, and argon is used as a protective atmosphere.
4. The nitrogen-doped carbon-supported Mo/Pt alloy catalyst according to claim 1, wherein: the calcination temperature is 670-820 ℃.
5. The nitrogen-doped carbon-supported Mo/Pt alloy catalyst according to claim 4, wherein: the calcination time is 10-60min.
6. The nitrogen-doped carbon-supported Mo/Pt alloy catalyst according to claim 1, wherein: the total metal loading is 1-6mg/25mg polypyrrole.
7. The nitrogen-doped carbon-supported Mo/Pt alloy catalyst according to claim 6, wherein: the mole ratio of Mo to Pt is 2-1:1-3.
8. Use of a nitrogen-doped carbon-supported Mo/Pt alloy catalyst according to any one of claims 1 to 7 as a redox electrocatalyst.
9. A fuel cell, characterized in that: wherein the catalyst is a nitrogen-doped carbon-supported Mo/Pt alloy catalyst according to any one of claims 1 to 7.
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