CN111933960B

CN111933960B - PtCo @ N-GNS catalyst and preparation method and application thereof

Info

Publication number: CN111933960B
Application number: CN202010828931.6A
Authority: CN
Inventors: 袁群惠; 高姣姣; 陈伊麦; 桂雅雯
Original assignee: Shenzhen Graduate School Harbin Institute of Technology
Current assignee: Shenzhen Graduate School Harbin Institute of Technology
Priority date: 2020-08-18
Filing date: 2020-08-18
Publication date: 2022-01-18
Anticipated expiration: 2040-08-18
Also published as: CN111933960A

Abstract

The invention relates to a PtCo @ N-GNS catalyst, and a preparation method and application thereof. The invention adopts zinc metal zeolite imidazole compound in Co²⁺And Pt⁴⁺The hydrolysis is carried out at room temperature in the presence of the acid, and the acid is prepared by combining the processes of tubular furnace sintering and the like. The material is characterized in that more holes are generated by evaporation of zinc metal, so that more active sites are exposed out of the material; in addition, the cobalt-platinum alloy particles wrapped by the graphene layer can effectively inhibit the corrosion of the alloy, and further improve the catalytic stability of the material. The material is modified on a glassy carbon electrode, and the mass activities of oxygen reduction and ethanol oxidation of the optimal material are respectively measured by cyclic voltammetry and linear scanning voltammetry

And

the invention has simple process and low cost, and the catalyst shows far higher catalytic activity and durability than commercial platinum/carbon catalysts, thereby having good application prospect.

Description

PtCo @ N-GNS catalyst and preparation method and application thereof

Technical Field

The invention relates to the technical field of fuel cells, in particular to a PtCo @ N-GNS catalyst and a preparation method and application thereof.

Background

Fuel cells using hydrogen or small-molecule organic substances as fuel are considered to be the most promising candidate for the next generation of clean energy systems due to their advantages of high energy conversion efficiency and low toxicity. The key to the development of fuel cell technology is the study of highly efficient and stable electrocatalysts for anode fuel oxidation reactions and cathode Oxygen Reduction Reactions (ORR). It is well known that commercial Pt/C and other noble metal Pt-based catalysts and their alloys are considered the most exotic fuel cell electrocatalysts. However, large-scale application of Pt/C is limited due to cost and stability issues. Therefore, the development of low-cost, high-catalytic-activity catalysts is of great importance for the technological development of future fuel cells.

Although the Pt-based catalyst has problems of high price, limited resources, easy poisoning, etc., the Pt-based catalyst is still considered as the best catalyst for fuel cells from the viewpoint of practical value. Currently, cost reduction, catalytic activity improvement and durability enhancement of Pt-based catalysts are mainly achieved from two aspects: (1) a Pt-based alloy catalyst; (2) a monodisperse Pt catalyst was prepared. Alloying is an important means for improving the catalytic performance of Pt, and the Pt and transition metal are alloyed, so that the lattice spacing between Pt and Pt can be shortened, the affinity between an intermediate product and an active site in the oxygen reduction process is reduced, and the oxygen reduction performance is further improved. The preparation of the monodisperse Pt or the monoatomic disperse Pt can improve the utilization rate of the noble metal, thereby reducing the cost of the catalyst. In addition, the alloy particles coated by the graphene can effectively inhibit the dissolution of metal, thereby improving the stability of the catalyst.

Disclosure of Invention

The invention aims to provide a PtCo @ N-GNS catalyst with high-efficiency dual functions of oxygen reduction and ethanol oxidation, and a preparation method and application thereof, aiming at the defects of the fuel cell catalyst in the prior art.

According to the preparation method, ZIF-8 is used as a template, potassium chloroplatinate and cobalt nitrate are used as a platinum source and a cobalt source respectively, a metal-organic framework material (PtCo @ ZIF-8) containing Pt and Co bimetal is prepared by adopting a simple hydrolysis reaction, and the nitrogen-doped carbon-coated platinum-cobalt nano-particles (PtCo @ N-GNS) are obtained by further heat treatment. The nano composite material prepared by the method has the advantages of good chemical stability, excellent conductivity, higher specific surface area and the like, and can improve the electrochemical performance of the material; meanwhile, the carbon layer is coated to effectively relieve the agglomeration problem of metal particles, so that the obtained nano particles are uniformly dispersed on the graphitized carbon nano sheet, the structural stability of the PtCo @ N-GNS nano composite material is ensured, and the catalytic activity of the PtCo particles is also ensured.

The technical scheme adopted for solving the technical problems of the invention is as follows:

firstly, the invention provides a preparation method of a low platinum-loaded PtCo @ N-GNS bifunctional catalyst, which comprises the following steps:

step one, synthesizing a zeolite imidazolate framework material ZIF-8;

dispersing cobalt salt, platinum salt solution and ZIF-8 in the solution, stirring, centrifuging, and drying in vacuum to obtain PtCo @ ZIF-8;

step three, placing the PtCo @ ZIF-8 obtained in the step two in a tubular furnace to calcine to obtain the PtCo @ N-GNS loaded by the nitrogen-doped carbon nano material;

and step four, soaking the material obtained in the step three in an acid solution to obtain the high-performance catalyst PtCo @ N-GNS.

Preferably, in the first step, zinc nitrate hexahydrate and 2-methylimidazole are used as raw materials for synthesizing ZIF-8, methanol is used as a solvent for dispersing the raw materials, the molar ratio of the metal salt to the ligand is 1:4, the reaction time is 24 hours, and the stirring speed is 500 rpm; the rotation speed of centrifugal separation is 8000rpm, the washed solvent is methanol, and the washing times are three times; the product obtained was dried under vacuum at 60 ℃ for 12 h.

Preferably, in the second step, the cobalt salt solution is cobalt nitrate hexahydrate, the platinum salt solution is potassium chloroplatinate, the mass ratio of the carrier ZIF-8 to the cobalt nitrate hexahydrate is 1: 1.2-1: 3, and the mass of the potassium chloroplatinate is 0.01 g; dispersing a carrier and cobalt nitrate, wherein a solvent of potassium chloroplatinate is deionized water; the reaction time is 24 h; the stirring speed is 500 rpm; the rotation speed of centrifugal separation is 8000 rpm; the washing solvent is deionized water and absolute ethyl alcohol; the number of washes is three; the product was dried under vacuum at 60 ℃ for 12 h.

Through a large number of experiments, it was found that, particularly preferably, with 0.01g of potassium chloroplatinate and 1.5g of cobalt nitrate hexahydrate, ZIF-8 crystalline powder (0.65g), the catalyst exhibited an optimum ORR performance and EOR performance, with the greatest improvement in performance.

Preferably, in the third step, the calcined PtCo @ ZIF-8 is PtCo @ ZIF-8 with different cobalt contents, and N is maintained during calcination₂And (3) atmosphere, wherein the calcining temperature is 700-1000 ℃, the calcining time is 2h, and the heating rate is 5 ℃/min.

Through a large number of experiments, it is found that particularly preferably, the temperature is low, Zn in the material can exist in a large amount and covers active sites, the structure of the material is damaged due to the high temperature, the active sites are greatly lost, the optimal temperature is 800 ℃, and the obtained active sites show the optimal ORR performance and EOR performance.

Preferably, in the fourth step, the hydrochloric acid concentration is 2.0mol/L, and the acid etching time is 12 h.

The invention further provides a low platinum-loaded PtCo @ N-GNS bifunctional catalyst, which is prepared by the preparation method. The PtCo alloy and the Co nanoparticles with high dispersion and high catalytic activity are formed on the nitrogen-doped carbon nanosheet.

The invention further provides the application of the catalyst in the catalytic reaction of the ethanol fuel cell, the catalyst is used for the reaction of the ethanol fuel cell, the ethanol oxidation reaction is carried out at the anode, and the oxygen reduction reaction is carried out at the cathode. Compared with commercial Pt/C, the PtCo @ N-GNS prepared by the invention has good catalytic activity, stability, durability and methanol toxicity resistance.

Compared with the prior art, the invention has the advantages that:

1. according to the invention, nitrogen sources and zinc salts with rich sources are utilized to prepare the nitrogen-doped porous carbon material with rich pore structures. The method has the advantages of simple preparation process, abundant and controllable raw materials, and high large-scale production value.

2. In the high-temperature calcination process, the nitrogen-doped carbon generated in the catalyst carrier has reducibility, does not need an additional reducing agent, and can reduce Pt and Co metal ions in situ.

3. Compared with commercial Pt/C, the PtCo @ N-GNS prepared by the invention has good catalytic activity, stability, durability and CO or intermediate product toxicity resistance.

Drawings

FIG. 1 is an X-ray diffraction pattern of the first, second, third, and fourth examples;

FIG. 2 is a scanning electron micrograph of PtCo @ N-GNS-3 of example III;

FIG. 3 is a transmission electron micrograph of PtCo @ N-GNS-3 of example III;

FIG. 4 is a graph showing oxygen reduction polarization curves of the catalysts prepared in example one, example two, example three, example four and comparative example 1 and commercial Pt/C;

FIG. 5 is a plot of cyclic voltammograms of ethanol oxidation of the catalysts prepared in examples one, two, and three and commercial Pt/C;

FIG. 6 is a graph showing oxygen reduction polarization curves of catalysts prepared in example five, example six, example seven and example eight;

FIG. 7 is the cyclic voltammogram of ethanol oxidation of the catalysts prepared in example five, example six, example seven and example eight.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below by way of examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

The invention provides a preparation method of a low-platinum-supported PtCo @ N-GNS bifunctional catalyst, which comprises the following steps of:

step one, synthesizing a zeolite imidazole ester framework material ZIF-8, dispersing zinc nitrate hexahydrate and 2-methylimidazole in methanol, wherein the molar ratio of metal salt to ligand is 1:4, the reaction time is 24 hours, and the stirring speed is 500 rpm; the rotation speed of centrifugal separation is 8000rpm, the washed solvent is methanol, and the washing times are three times; the temperature of the obtained product dried in vacuum was 60 ℃ and the drying time was 12 h.

Dispersing cobalt salt and platinum salt with certain mass into the solution, adding ZIF-8, and fully mixing at a stirring reaction speed of 500rpm for 24 hours; the rotational speed of centrifugal separation is 8000rpm, the solvent washed is deionized water, the number of washing times is three; the temperature of the obtained product dried in vacuum was 60 ℃ and the drying time was 12 h.

Thirdly, placing the synthesized PtCo @ ZIF-8 in a tubular furnace to calcine to obtain the N-doped carbon nanomaterial loaded PtCo @ N-GNS; when preparing the PtCo @ N-GNS material, the precursor is PtCo @ ZIF-8 with different Co contents, and N is kept in the calcining process₂And (3) the atmosphere, the calcining temperature is 700-1000 ℃, the calcining time is 2h, and the heating rate is 5 ℃/min.

The invention is further illustrated by the following specific examples.

The first embodiment is as follows:

(1) synthesis of ZIF-8

4.42g of zinc nitrate hexahydrate and 4.92g of 2-methylimidazole were dissolved in 25mL of methanol to prepare clear solutions, respectively. After the two solutions are uniformly mixed, reacting for 24 hours at the rotating speed of 500 rpm; centrifuging at 8000rpm, and washing with methanol for three times; the product was dried in vacuo at 60 ℃ for 12 h.

(2) Synthesis of PtCo @ ZIF-8

0.01g of potassium chloroplatinate and 0.75g of cobalt nitrate hexahydrate were dispersed in 50mL of deionized water, while ZIF-8 crystal powder (0.65g) was dispersed in another 50mL of deionized water, and finally the two solutions were mixed well and stirred for 24 hours. The product is washed with deionized water for three times and dried in vacuum at 60 ℃ for 12 h.

(3) Synthesis of PtCo @ N-GNS

Weighing a proper amount of the product, placing the product in a tube furnace, heating to 800 ℃ at a heating rate of 5 ℃/min under the protection of nitrogen, and keeping for 2 hours to obtain a sintered product. And (3) soaking the sintered product in 2M HCl for 12h, removing unreacted metal, performing centrifugal separation three times by using deionized water, and drying in a vacuum drying oven at 60 ℃ for 12h to obtain a final sample, namely PtCo @ N-GNS-1.

Example two:

(1) synthesis of ZIF-8

(2) Synthesis of PtCo @ ZIF-8

0.01g of potassium chloroplatinate and 1.0g of cobalt nitrate hexahydrate were dispersed in 50mL of deionized water, while ZIF-8 crystal powder (0.65g) was dispersed in another 50mL of deionized water, and finally the two solutions were mixed well and stirred for 24 hours. The product is washed with deionized water for three times and dried in vacuum at 60 ℃ for 12 h.

(3) Synthesis of PtCo @ N-GNS

Weighing a proper amount of the product, placing the product in a tube furnace, heating to 800 ℃ at a heating rate of 5 ℃/min under the protection of nitrogen, and keeping for 2 hours to obtain a sintered product. And (3) soaking the sintered product in 2M HCl for 12h, removing unreacted metal, performing centrifugal separation three times by using deionized water, and drying in a vacuum drying oven at 60 ℃ for 12h to obtain a final sample, namely PtCo @ N-GNS-2.

Example three:

(1) synthesis of ZIF-8

(2) Synthesis of PtCo @ ZIF-8

0.01g of potassium chloroplatinate and 1.5g of cobalt nitrate hexahydrate were dispersed in 50mL of deionized water, while ZIF-8 crystal powder (0.65g) was dispersed in another 50mL of deionized water, and finally the two solutions were mixed well and stirred for 24 hours. The product is washed with deionized water for three times and dried in vacuum at 60 ℃ for 12 h.

(3) Synthesis of PtCo @ N-GNS

Weighing a proper amount of the product, placing the product in a tube furnace, heating to 800 ℃ at a heating rate of 5 ℃/min under the protection of nitrogen, and keeping for 2 hours to obtain a sintered product. And (3) soaking the sintered product in 2M HCl for 12h, removing unreacted metal, performing centrifugal separation three times by using deionized water, and drying in a vacuum drying oven at 60 ℃ for 12h to obtain a final sample, namely PtCo @ N-GNS-3.

Example four:

(1) synthesis of ZIF-8

(2) Synthesis of PtCo @ ZIF-8

0.01g of potassium chloroplatinate and 2.0g of cobalt nitrate hexahydrate were dispersed in 50mL of deionized water, while ZIF-8 crystal powder (0.65g) was dispersed in another 50mL of deionized water, and finally the two solutions were mixed well and stirred for 24 hours. The product is washed with deionized water for three times and dried in vacuum at 60 ℃ for 12 h.

(3) Synthesis of PtCo @ N-GNS

Weighing a proper amount of the product, placing the product in a tube furnace, heating to 800 ℃ at a heating rate of 5 ℃/min under the protection of nitrogen, and keeping for 2 hours to obtain a sintered product. And (3) soaking the sintered product in 2M HCl for 12h, removing unreacted metal, performing centrifugal separation for three times by using pure water, and drying in a vacuum drying oven at 60 ℃ for 12h to obtain a final sample, namely PtCo @ N-GNS-4.

Wherein, FIG. 1 is an X-ray diffraction diagram of the first, second, third and fourth embodiments; FIG. 2 is a scanning electron micrograph of PtCo @ N-GNS-3 of example III; FIG. 3 is a transmission electron micrograph of PtCo @ N-GNS-3 of example III.

Example five:

(1) synthesis of ZIF-8

(2) Synthesis of PtCo @ ZIF-8

(3) Synthesis of PtCo @ N-GNS-700

Weighing a proper amount of the product, placing the product in a tube furnace, heating to 700 ℃ at a heating rate of 5 ℃/min under the protection of nitrogen, and keeping for 2 hours to obtain a sintered product. And (3) soaking the sintered product in 2M HCl for 12h, removing unreacted metal, performing centrifugal separation for three times by using pure water, and drying in a vacuum drying oven at 60 ℃ for 12h to obtain a final sample, namely PtCo @ N-GNS-700.

Example six:

(1) synthesis of ZIF-8

(2) Synthesis of PtCo @ ZIF-8

(3) Synthesis of PtCo @ N-GNS-800

Weighing a proper amount of the product, placing the product in a tube furnace, heating to 800 ℃ at a heating rate of 5 ℃/min under the protection of nitrogen, and keeping for 2 hours to obtain a sintered product. And (3) soaking the sintered product in 2M HCl for 12h, removing unreacted metal, performing centrifugal separation three times by using deionized water, and drying in a vacuum drying oven at 60 ℃ for 12h to obtain a final sample, namely PtCo @ N-GNS-800.

Example seven:

(1) synthesis of ZIF-8

(2) Synthesis of PtCo @ ZIF-8

(3) Synthesis of PtCo @ N-GNS-900

Weighing a proper amount of the product, placing the product in a tube furnace, heating to 900 ℃ at a heating rate of 5 ℃/min under the protection of nitrogen, and keeping for 2 hours to obtain a sintered product. And (3) soaking the sintered product in 2M HCl for 12h, removing unreacted metal, performing centrifugal separation for three times by using pure water, and drying in a vacuum drying oven at 60 ℃ for 12h to obtain a final sample, namely PtCo @ N-GNS-900.

Example eight:

(1) synthesis of ZIF-8

(2) Synthesis of PtCo @ ZIF-8

(3) Synthesis of PtCo @ N-GNS-1000

Weighing a proper amount of the product, placing the product in a tube furnace, heating to 1000 ℃ at a heating rate of 5 ℃/min under the protection of nitrogen, and keeping the temperature for 2 hours to obtain a sintered product. And (3) placing the sintered product in 2M HCl for soaking for 12h, removing unreacted metal, performing centrifugal separation for three times by using pure water, and placing the product in a vacuum drying oven at 60 ℃ for drying for 12h to obtain a final sample, namely PtCo @ N-GNS-1000.

Comparative example one:

(1) synthesis of ZIF-8

(2) Synthesis of Co @ ZIF-8

(3) Synthesis of Co @ N-GNS

Weighing a proper amount of the product, placing the product in a tube furnace, heating to 800 ℃ at a heating rate of 5 ℃/min under the protection of nitrogen, and keeping for 2 hours to obtain a sintered product. And (3) placing the sintered product in 2M HCl for soaking for 12h, removing unreacted metal, performing centrifugal separation for three times by using pure water, and placing the product in a vacuum drying oven at 60 ℃ for drying for 12h to obtain a final sample, wherein the final sample is marked as Co @ N-GNS.

The catalytic materials prepared in the respective examples and comparative examples were tested for their performance.

Electrochemical testing was performed using a three-electrode system. The working electrode was a catalyst coated glassy carbon electrode, where the catalyst was the catalyst prepared in examples 1-8, commercial Pt/C, comparative example 1, the counter electrode was a platinum sheet, and the reference electrode was an Ag/AgCl electrode. When ORR is tested, the electrolyte is 0.1M HClO saturated with oxygen₄An aqueous solution. The electrolyte for testing EOR is 0.5M H₂SO₄And 0.5M C₂H₅Mixed solution of OH. The preparation steps of the catalyst thin layer on the electrode are as follows: taking 4mg of catalyst, adding 300 mu L of ethanol and 100 mu L of Nafion solution (0.5 wt.%), carrying out ultrasonic dispersion for 30min, taking 4 mu L of uniformly dispersed suspension liquid by using a 10 mu L liquid-transferring gun, dripping the suspension liquid on a smooth glassy carbon electrode, and carrying out infrared drying to test the electrochemical performance, wherein the test result is shown in figures 4-7.

From FIG. 4 at 0.1M HClO under oxygen saturation₄Different Co obtained in solutionThe ORR graph of the content catalyst can be seen: of the six catalysts comprising commercial Pt/C, the catalyst PtCo @ N-GNS-3 exhibited an optimal ORR performance at a Co content of 1.5g, with a half-wave potential of 0.93V, over the commercial 20% Pt/C catalyst (0.85V at half-wave potential).

From FIG. 5 at 0.5M H₂SO₄And 0.5M C₂H₅The CV curves of the EOR of the different Co content catalysts obtained in the mixed OH solution can be seen: of the four catalysts comprising commercial Pt/C, at a Co content of 1.5g, the catalyst PtCo @ N-GNS-3 exhibited an optimum EOR performance with a quality activity of up to

Far surpass the commercial 20 percent Pt/C catalyst (the mass activity is

)。

In addition, from FIG. 6, the oxygen saturation is at 0.1M HClO₄The ORR polarization curves of the catalysts obtained in the solution at different calcination temperatures and the CV results of EOR in fig. 7 show that at a lower temperature, Zn in the material exists in a large amount and covers active sites, and that at a higher temperature, the structure of the material is damaged, the active sites are greatly lost, and the optimal temperature is 800 ℃.

The above description is only exemplary of the present invention and should not be taken as limiting the invention, and any modifications, equivalents, improvements, etc. that are made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims

1. A preparation method of a PtCo @ N-GNS catalyst is characterized in that the catalyst comprises two-dimensional porous nitrogen-doped carbon, and a PtCo alloy and metal Co coated inside the porous nitrogen-doped carbon, and comprises the following steps:

step one, synthesizing a zeolite imidazolate framework material ZIF-8;

dispersing cobalt salt, platinum salt solution and ZIF-8 in the solution, stirring, centrifuging, washing, and drying in vacuum to obtain PtCo @ ZIF-8: the dosage of potassium chloroplatinate, cobalt nitrate hexahydrate and ZIF-8 crystal powder is respectively as follows: 0.01g of potassium chloroplatinate and 1.5g of cobalt nitrate hexahydrate, 0.65g of ZIF-8 crystal powder; dispersing a carrier and cobalt nitrate, wherein a solvent of potassium chloroplatinate is deionized water; the reaction time is 24 h; the stirring speed is 500 rpm; the rotation speed of centrifugal separation is 8000 rpm; the washing solvent is deionized water and absolute ethyl alcohol; the number of washes is three; the product is dried for 12 hours at the vacuum drying temperature of 60 ℃;

and step four, soaking the material obtained in the step three in an acid solution to obtain the catalyst PtCo @ N-GNS.

2. The preparation method of claim 1, wherein, in the first step, the raw materials for synthesizing ZIF-8 are zinc nitrate hexahydrate and 2-methylimidazole, the solvent for dispersing the raw materials is methanol, the molar ratio of the metal salt to the ligand is 1:4, the reaction time is 24 hours, and the stirring speed is 500 rpm; the rotation speed of centrifugal separation is 8000rpm, the washed solvent is methanol, and the washing times are three times; the product obtained was dried under vacuum at 60 ℃ for 12 h.

3. The method of claim 1, wherein in step three, N is maintained during calcination₂And (3) atmosphere, wherein the calcining temperature is 700-1000 ℃, the calcining time is 2h, and the heating rate is 5 ℃/min.

4. The method of claim 3, wherein the temperature of the calcination is 800 ℃.

5. The method according to claim 1, wherein in the fourth step, the hydrochloric acid concentration is 2.0mol/L, and the acid etching time is 12 hours.

6. A PtCo @ N-GNS catalyst, characterized by being prepared by the preparation method of any one of claims 1 to 5.

7. Use of the catalyst of claim 6 in a catalytic reaction in an ethanol fuel cell, wherein the oxidation of ethanol takes place at the anode and the reduction of oxygen takes place at the cathode.