CN110611105A - The preparation method of ORR catalyst - Google Patents

Abstract

The invention provides a preparation method of an ORR catalyst. The preparation method of the ORR catalyst comprises the following steps: 1) making a precursor of a cobalt-containing polynitrogen metal-organic framework material; 2) dispersing the precursor in an ethylene glycol solution containing chloroplatinic acid, and performing microwave synthesis/extraction reaction , to prepare a cobalt polynitrogen metal organic framework material containing platinum participating in the post-coordination; 3) performing a calcination treatment on the cobalt polynitrogen metal organic framework material participating in the platinum post-coordination to obtain an ORR catalyst. Using Pt-enhanced multi-nitrogen imidazole carboxylic acid cobalt-based metal-organic framework materials to prepare electrocatalysts by redox, the operation process is simple; at the same time, the platinum content in the catalyst is reduced, and the prepared catalyst metal-organic framework has a microporous structure. It is helpful for the transmission of protons and gases, and the product has high catalytic performance.

Description

The preparation method of ORR catalyst

technical field

The invention belongs to the technical field of oxidation-reduction electrocatalysis, and in particular relates to a preparation method of an ORR catalyst.

Background technique

Since the development of human civilization, material and spiritual civilization have been highly developed. As human society continues to develop at a high speed, the importance of energy is self-evident. With the continuous use of the three major ore energy sources, problems such as energy reserves, over-exploitation and environmental pollution have become more and more serious. Although every innovation and breakthrough in energy technology has had a huge impact on the development of productivity and social change, all these social advances today are built on the basis of extensive use of fossil fuels. Facing the demand for energy from global economic and population growth, the depletion of traditional energy sources, and the deteriorating human living environment, the development of clean, renewable and new energy is the only way to maintain sustainable human development.

Hydrogen energy, with many advantages such as cleanness, high efficiency and environmental friendliness, is considered to be an ideal energy source in the 21st century. In addition, the main body of hydrogen exists in the form of compound water, and about 70% of the earth's surface is covered by water, so hydrogen is an "inexhaustible and inexhaustible" energy source. Because of this, the United States, Japan and other countries are vigorously developing their own hydrogen fuel cells. For example, as early as 2002, the United States formulated a national hydrogen energy development roadmap, and Japan is also implementing the New Sunshine Plan to develop a hydrogen energy economy. Fuel cell, as a hydrogen energy utilization technology, is an energy conversion device that can directly convert chemical energy into electrical energy, and has high conversion efficiency. Its electrochemical reaction process is the process of hydrogen-oxygen reaction to generate water.

Proton exchange membrane fuel cell (PEMFC, proton exchange membrane fuel cell) is a green, high-efficiency, high-energy-density energy conversion device, which can directly convert chemical energy into electrical energy, and has a fast start-up, no pollution, and a conversion efficiency of up to 40 %. The core component of PEMFC is the membrane electrode (MEA, membrane electrode assemblies), which is made of a catalytically active proton exchange membrane and a gas diffusion layer (GDL, gas diffusion layer) by hot pressing. As the place where the electrochemical reaction occurs, the performance of the MEA directly determines the conversion efficiency of the fuel cell, and also determines the performance, life and cost of the product. The electrochemical reaction performance of MEA is mainly determined by the catalytic activity, specific surface area and electrochemical stability of the catalyst. According to the report of the US Department of Energy (DOE, Department of Energy), among all the costs of an 80 kW automotive PEMFC stack, platinum (Pt, platinum) as a redox catalyst in the catalyst layer accounts for 17% of it. Therefore, under the background of "high current density, low platinum loading, and low humidification", how to carry out a new design on the catalytic layer (CL, Catalyst Layer) to achieve high power density while reducing platinum loading has become the current PEMFC the forefront of research.

Oxidation-reduction reaction (ORR) is the fundamental reaction at the cathode in proton exchange membrane fuel cells, and commercial Pt/C catalysts are currently the most commonly used ORR electrocatalysts. However, the limited reserves of Pt in nature and the high price prevent large-scale commercial application of fuel cells. In the past decades, scientists have developed different kinds of electrocatalysts, for example, electrocatalysts of non-noble metals and metal-free materials. Among these ORR catalytic materials, metal-organic frameworks (MOFs) have been applied in proton conduction, electrocatalysis, etc. In the field, heteroatoms (B, N, S, P, etc.) prepared from metal-organic frameworks as precursors can be doped into carbon substrates or combined with metal/metal oxides to enhance electrocatalytic activity, but the effects are not satisfactory.

Contents of the invention

Therefore, the technical problem to be solved by the present invention is to provide a method for preparing an ORR catalyst, which can reduce the Pt content in the catalyst and have higher catalytic performance.

In order to solve the above problems, the present invention provides a method for preparing an ORR catalyst, comprising the following steps:

1) Making precursors of cobalt-containing polynitrogen metal-organic framework materials;

2) Disperse the precursor in an ethylene glycol solution containing chloroplatinic acid, and perform microwave synthesis/extraction reaction to prepare a cobalt polynitrogen metal-organic framework material containing platinum participating in post-coordination;

3) The cobalt polynitrogen metal-organic framework material coordinated after platinum participation is calcined to obtain an ORR catalyst.

Preferably, step 1) is:

Dissolve the cobalt salt and 2-(p-N-imidazolyl)phenyl-1H-4,5-imidazoledicarboxylic acid ligand in a mixed solvent, adjust the pH value of the solution to be acidic, and perform a hydrothermal reaction to obtain Cobalt polynitrogen type metal organic framework material precursor.

Preferably, the pH of the solution is adjusted to 2-4, and the hydrothermal reaction takes place at 140-155° C. for 48-96 hours.

Preferably, the cobalt salt is CoCl ₂ ·6H ₂ O or Co(NO ₃ ) ₂ ·6H ₂ O, and/or the mixed solvent is mixed with water and acetonitrile with a volume ratio of 4~8:1~3 constitute.

Preferably, in step 2), the molar ratio of the precursor to the ethylene glycol solution containing chloroplatinic acid is 1:0.01-1.

Preferably, the precursor is dispersed in an ethylene glycol solution containing chloroplatinic acid, and heated to 110-120° C. in an inert gas atmosphere to perform microwave synthesis/extraction reaction for 15-20 minutes.

Preferably, after the microwave synthesis/extraction reaction is completed, the reaction system is cooled to 30-45° C., and the reaction system is successively centrifuged, washed with water and vacuum-dried.

Preferably, in step 3), the platinum-coordinated cobalt polynitrogen metal-organic framework material is heated to 300-500° C. in an inert gas atmosphere and kept for 1-2 hours.

Preferably, the heating process is carried out at a heating rate of 2-3°C/min.

Preferably, the calcined product is sequentially subjected to ultrasonic washing with an organic solvent, water washing to neutrality and drying. .

A preparation method of an ORR catalyst provided by the present invention comprises the following steps: 1) making a precursor of a cobalt-containing polynitrogen metal-organic framework material; 2) dispersing the precursor in an ethylene glycol solution containing chloroplatinic acid, Microwave synthesis/extraction reaction is carried out to prepare a cobalt polynitrogen metal organic framework material containing platinum after coordination; 3) the cobalt polynitrogen metal organic framework material with platinum participation and coordination is calcined to obtain an ORR catalyst. Using Pt-enhanced multi-nitrogen imidazole carboxylic acid cobalt-based metal-organic framework materials to prepare electrocatalysts by redox, the operation process is simple; at the same time, the platinum content in the catalyst is reduced, and the prepared catalyst metal-organic framework has a microporous structure. It is helpful for the transmission of protons and gases, and the product has high catalytic performance.

Description of drawings

Fig. 1 is the XRD pattern of the cobalt-based metal-organic framework synthesized in the embodiment of the present invention; the measured curve is a synthetic product, and the simulated curve is a simulated product;

Fig. 2 is the SEM image of Co-MNMOF, Pt/Co-MNMOF and Pt/Co-NC prepared in the embodiment of the present invention, corresponding to Fig. 2(a), Fig. 2(b) and Fig. 2(c);

Fig. 3 is the HR-TEM picture (high-resolution transmission electron microscope picture) of the Pt/Co-NC nanoparticle that the embodiment of the present invention prepares; It can be seen that the Pt/Co-NC catalyst particles are uniformly dispersed;

Fig. 4 is Co-MNMOF of the embodiment of the present invention, Pt/Co-MNMOF, Pt/Co-NC catalyst in N _The comparison of the cyclic voltammetry (CV) curve figure in the saturated _0.1MHClO electrolyte;

Fig. 5 is the Pt/Co-NC of the embodiment of the present invention and commercial ₂₀ %Pt/C catalyst in N ₂ saturated 0.1M HClO in the electrolytic solution CV figure comparison;

Fig. 6 is the comparison of the oxygen reduction (ORR) curve of Co-MNMOF, Pt/Co-MNMOF, Pt/Co-NC catalyst in _O2 saturated _0.1MHClO electrolyte of the embodiment of the present invention;

Fig. 7 is a comparison of the oxygen reduction (ORR) of the Pt/Co-NC of the embodiment of the present invention and the commercial 20% Pt/C catalyst in the O ₂ saturated 0.1M HClO ₄ electrolyte.

Detailed ways

In order to reduce the amount of limited Pt resources, the present invention provides a method for preparing a redox electrocatalyst based on Pt-enhanced multi-nitrogen imidazole carboxylic acid cobalt-based metal-organic framework materials. The basic reaction principle of the preparation method is shown in the following equation:

Chemical formula: [Co(p-IPhHIDC)] _n

Chemical formula: Pt/Co-MNMOF

The technical scheme of the preparation method of the ORR catalyst of the present invention is as follows, comprising the following steps:

1) Dissolve the cobalt salt and 2-(p-N-imidazolyl)phenyl-1H-4,5-imidazoledicarboxylic acid ligand in water and acetonitrile solvent, and add acid to adjust the pH value of the solution after ultrasonic and stirring 2 to 4, and then hydrothermal reaction occurs at a constant temperature of 140 to 155°C for 48 to 96 hours; after cooling to room temperature, the obtained product is washed in turn and dried naturally to form a black-green transparent cobalt-containing multi-nitrogen metal organic compound. Framework material precursor (chemical formula: [Co(p-IPhHIDC)]n);

2) The precursor material [Co(p-IPhHIDC)] _n prepared in step 1) was thoroughly ground and ultrasonically dispersed in an ethylene glycol solution containing chloroplatinic acid (H ₂ PtCl ₆ 6H ₂ O), and the The mixed solution is placed in a microwave synthesis extraction reactor at 110-120°C, reacted intermittently for 15-20 minutes, and uses N ₂ as a protective gas; take it out after the temperature is cooled to about 30-45°C, and the reacted solution in turn After centrifugation, washing and vacuum drying, the Pt/Co-MNMOF black solid powder with Pt participating in the coordination is obtained;

3) Under N ₂ atmosphere, the Pt/Co-MNMOF powder obtained in step 2) was calcined at low temperature for 1-2 hours, the obtained powder was ultrasonically washed with an organic solvent, and then repeatedly centrifuged with water until neutral, and the target product Pt/Co-MNMOF was obtained after drying. Co-NC.

Wherein, in step 1), in the mixed solvent of water and acetonitrile, the mixing volume ratio of water and acetonitrile is 4-8: 1-3.

In step 2), the molar ratio of the precursor to the chloroplatinic acid ethylene glycol solution is 1:0.01-1.

In step 3), the Pt/Co-MNMOF black solid powder is placed in a _N2 atmosphere tube furnace, heated to 300-500°C at a heating rate of 2-3°C/min, kept for 1.5h, and then heated at a rate of 1°C/min The cooling rate is to cool to room temperature, and then wash. Wherein the used organic solvent of ultrasonic cleaning is acetone or ethanol.

In order to illustrate the purpose and technical solution of the present invention more clearly, specific examples will be described in detail below.

Example 1

1. Mix 0.05mmol, 11.9mg of CoCl ₂ 6H ₂ O and 0.03mmol, 8.9mg of 2-(pN-imidazolyl)phenyl-1H-4,5-imidazoledicarboxylic acid ligand (p-IPhH3IDC) Dissolve in 2mL of acetonitrile and 5mL of water, mix well, add concentrated HCl to adjust the pH to 2, and conduct a hydrothermal reaction at 150°C for 96 hours; after the reaction, the product obtained is centrifuged, washed with acetone three times, washed with water three times, and dried naturally at room temperature. A black-green transparent cobalt-containing polynitrogen-type metal-organic framework material was obtained. Figure 1 shows the XRD pattern of the obtained product.

2. After the material obtained in step 1 and the ethylene glycol solution of chloroplatinic acid are dispersed uniformly by ultrasonic at a molar ratio of 1:0.02, they are placed in a microwave synthesizer at 113°C under the protection of N ₂ , and the 10s/10s intermittent Microwave reaction for 16 minutes to reduce H ₂ PtCl ₆ to Pt simple substance; in order to prevent the metal (Co or Pt) from being oxidized, take out the solution after the temperature of the solution reaches 40°C, and then repeatedly centrifuge the solution three times, wash with water, and vacuum at 80°C After drying, the Pt/Co-MNMOF black solid powder was obtained.

3. Put the Pt/Co-MNMOF black solid powder in a _N2 atmosphere tube furnace, heat it to 400°C at a heating rate of 3°C/min, keep it for 1.5h, and then cool it to room temperature at a cooling rate of 1°C/min. The obtained powder was washed with acetone, then washed with deionized water and ultrapure water until neutral, and dried in a vacuum oven at 80°C to obtain the Pt/Co-NC electrocatalyst. Figure 2 shows the SEM images of Co-MNMOF image (a), Pt/Co-MNMOF image (b) and Pt/Co-NC electrocatalyst image (c), respectively. Figure 3 is a TEM image of the Pt/Co-NC catalyst.

From the XRD pattern of step 1) product [Co(p-IPhHIDC)]n detected in Figure 1, it can be seen that the peak position of the synthesized product is basically consistent with the simulated peak position, verifying the purity of the product.

However, it can be seen from Figure 2 that the morphology of Figure 2(a) is microspheres formed by flakes; it can be seen from Figures 2(b) and 2(c) that the addition of Pt atoms causes obvious damage to the microspheres , which increases its specific surface area, which can improve the electrocatalytic activity and the rapid conduction of protons.

It can be seen from Figure 3 that the Pt/Co-NC catalyst particles are uniformly dispersed.

Example 2

1. 0.05mmol, 11.9mg of CoCl ₂ ·6H ₂ O and 0.03mmol, 8.9mg of 2-(pN-imidazolyl)phenyl-1H-4,5-imidazole dicarboxylic acid ligand (p-IPhH3IDC, ) was dissolved in 2mL of acetonitrile and 5mL of water, mixed evenly, adjusted to pH 4 by adding concentrated HCl, and hydrothermally reacted at 150°C for 96h; the product obtained after the reaction was centrifuged, washed three times with acetone, washed three times with water, and dried naturally at room temperature. That is, a black-green transparent cobalt-containing polynitrogen metal-organic framework (Co-MNMOF) is obtained.

2. After the precursor Co-MNMOF material and the ethylene glycol solution of chloroplatinic acid are dispersed uniformly by ultrasonic at a molar ratio of 1:0.05, they are placed in a microwave synthesizer at 113°C under the protection of N ₂ , and the 10s/10s intermittent Microwave reaction for 16 minutes to reduce H ₂ PtCl ₆ to Pt simple substance; in order to prevent the metal (Co or Pt) from being oxidized, take out the solution after the temperature of the solution reaches 40°C, and then repeatedly centrifuge the solution three times, wash with water, and vacuum at 80°C After drying, the Pt/Co-MNMOF black solid powder was obtained.

3. Put the Pt/Co-MNMOF black solid powder in a _N2 atmosphere tube furnace, heat it to 500°C at a heating rate of 2°C/min, keep it for 1.5h, and then cool it to room temperature at a cooling rate of 1°C/min. The obtained powder was washed with acetone, then washed with deionized water and ultrapure water until neutral, and dried in a vacuum oven at 80°C to obtain the Pt/Co-NC electrocatalyst.

Example 3

1. Mix 0.05mmol, 11.9mg of Co(NO ₃ ) ₂ ·6H ₂ O and 0.03mmol, 8.9mg of 2-(pN-imidazolyl)phenyl-1H-4,5-imidazoledicarboxylic acid ligand ( p-IPhH3IDC,) was dissolved in 2 mL of acetonitrile and 5 mL of water, mixed well, then added concentrated HCl to adjust the pH to 3, and hydrothermally reacted at 150°C for 96 hours; After natural drying, a black-green transparent cobalt-containing multi-nitrogen metal-organic framework (Co-MNMOF) is obtained.

2. After the precursor Co-MNMOF material and the ethylene glycol solution of chloroplatinic acid are dispersed uniformly by ultrasonic at a molar ratio of 1:0.1, they are placed in a microwave synthesizer at 113°C under the protection of N ₂ , and the 10s/10s intermittent Microwave reaction for 16 minutes to reduce H ₂ PtCl ₆ to Pt simple substance; in order to prevent the metal (Co or Pt) from being oxidized, take out the solution after the temperature of the solution reaches 40°C, and then repeatedly centrifuge the solution three times, wash with water, and vacuum at 80°C After drying, the Pt/Co-MNMOF black solid powder was obtained.

3. Put the Pt/Co-MNMOF black solid powder in a _N2 atmosphere tube furnace, heat it to 300°C at a heating rate of 2.3°C/min, keep it for 1.5h, and then cool it to room temperature at a cooling rate of 1°C/min. The obtained powder was washed with acetone, then washed with deionized water and ultrapure water until neutral, and dried in a vacuum oven at 80°C to obtain the Pt/Co-NC electrocatalyst.

The products obtained in the first stage of embodiment 2 and embodiment 3 are detected, and the results are similar to those shown in Figures 1, 2 and 3.

The Pt/Co-NC electrocatalysts prepared by all the above-mentioned examples are detected and compared, and the specific methods are as follows:

Add 150 μL of deionized water to 15 mg of Co-MNMOF, Pt/Co-MNMOF and Pt/Co-NC catalysts respectively, after completely soaking, then add 150 μL of Nafion (5wt%) solution and 4 mL of isopropanol, and obtain after ultrasonic dispersion Uniformly dispersed catalyst slurry; 15 μL of the slurry was drip-coated on the glassy carbon electrode, using a three-electrode system, the glassy carbon electrode loaded with the catalyst was used as the working electrode, the platinum electrode was used as the counter electrode, and the saturated calomel electrode was used as the reference electrode . The working electrode was placed in N ₂ and O ₂ saturated 0.1M HClO ₄ electrolyte for cyclic voltammetry (CV) test and redox (ORR) test, the results are shown in Figure 4, Figure 5, Figure 6 and Figure 7 shown.

It can be seen from Figure 4 that in the electrolyte saturated with _N2 , the adsorption peak areas of hydrogen oxidation in the cyclic voltammograms of Co-MNMOF, Pt/Co-MNMOF, and Pt/Co-NC catalysts are in the following order: Pt/Co -NC>Pt/Co-MNMOF>Co-MNMOF. It is confirmed by the CV diagram that the addition of Pt atoms increases the catalytic active area of Co-MNMOF, which is beneficial to the adsorption of _O2 on the catalyst surface.

It can be seen in Fig. 5 that the hydrogen oxidation adsorption peak area of the Pt/Co-NC catalyst is larger than that of the commercial 20% Pt/C catalyst. The mutual coordination between the bimetals exposes more active sites on the Pt/Co-NC catalyst.

It can be seen from Figure 6 that in the electrolyte saturated with O ₂ , the limiting current values of Co-MNMOF, Pt/Co-MNMOF, and Pt/Co-NC catalysts are (0.62V vs. SCE): Pt/Co -NC>Pt/Co-MNMOF>Co-MNMOF, confirmed by the oxygen reduction (ORR) diagram, the participation of Pt atoms enhanced the oxygen reduction ability of Co-MNMOF.

It can be seen from Figure 7 that the limiting current value (0.62V vs. SCE) of the Pt/Co-NC catalyst is greater than that of the 20% Pt/C catalyst. The Pt/Co-NC catalyst not only reduces the usage of Pt, but also enhances the proton transport due to the coordinated effect between the bimetals.

Those skilled in the art can easily understand that, on the premise of no conflict, the above-mentioned implementation manners can be freely combined and superimposed.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should be included in the protection of the present invention. within range. The above is only a preferred embodiment of the present invention, it should be pointed out that for those of ordinary skill in the art, without departing from the technical principle of the present invention, some improvements and modifications can also be made, these improvements and modifications It should also be regarded as the protection scope of the present invention.

Claims (10)

1. a preparation method of ORR catalyst, is characterized in that, comprises the following steps: 1) Making precursors of cobalt-containing polynitrogen metal-organic framework materials; 2) Disperse the precursor in an ethylene glycol solution containing chloroplatinic acid, and perform microwave synthesis/extraction reaction to prepare a cobalt polynitrogen metal-organic framework material containing platinum participating in post-coordination; 3) The cobalt polynitrogen metal-organic framework material coordinated after platinum participation is calcined to obtain an ORR catalyst. 2. preparation method according to claim 1, is characterized in that, step 1) is: Dissolve the cobalt salt and 2-(p-N-imidazolyl)phenyl-1H-4,5-imidazoledicarboxylic acid ligand in a mixed solvent, adjust the pH value of the solution to be acidic, and perform a hydrothermal reaction to obtain Cobalt polynitrogen type metal organic framework material precursor. 3. The preparation method according to claim 2, characterized in that the pH value of the solution is adjusted to 2-4, and the hydrothermal reaction takes place at 140-155° C. for 48-96 hours. 4. The preparation method according to claim 2 or 3, characterized in that, the cobalt salt is CoCl ₂ 6H ₂ O or Co(NO ₃ ) ₂ 6H ₂ O, and/or the mixed solvent is obtained by volume Mix water and acetonitrile with a ratio of 4-8:1-3. 5. The preparation method according to claim 1, characterized in that, in step 2), the molar ratio of the precursor to the ethylene glycol solution containing chloroplatinic acid is 1:0.01-1. 6. The preparation method according to claim 1 or 5, characterized in that the precursor is dispersed in an ethylene glycol solution containing chloroplatinic acid, heated to 110-120°C in an inert gas atmosphere for microwave synthesis/extraction reaction 15-20 minutes. 7 . The preparation method according to claim 6 , characterized in that, after the microwave synthesis/extraction reaction is completed, the reaction system is cooled to 30-45° C., and the reaction system is successively centrifuged, washed with water and vacuum-dried. 8. The preparation method according to claim 1, characterized in that, in step 3), the cobalt polynitrogen-type metal-organic framework material in which platinum participates in the post-coordination is heated to 300-500° C. in an inert gas atmosphere and kept for 1 ~2 hours. 9. The preparation method according to claim 8, characterized in that the heating process is carried out at a heating rate of 2-3°C/min. 10. The preparation method according to claim 8 or 9, characterized in that the calcined product is successively subjected to ultrasonic washing with an organic solvent, washing with water to neutrality and drying.