A 3D porous spherical carbon shell-supported transition metal single atom catalyst and its preparation method and application

Abstract

The present invention discloses a 3D porous spherical carbon shell-supported transition metal single-atom catalyst, a preparation method and application thereof, and belongs to the technical field of preparation of fuel cell electrocatalysts. The present invention synthesizes a metal skeleton catalyst with a three-dimensional spherical structure of a core-shell structure by a dual solvent induction technique, and the catalyst can retain a hollow porous spherical structure after high-temperature calcination. Specifically, a metal organic framework precursor is mixed with a spherical template solution of an external functional group to obtain a 3D spherical metal organic framework precursor solution divided into an outer shell and an inner core structure, and a uniformly dispersed 3D spherical metal organic framework is obtained by a dual solvent induction technique, and then heat-treated after centrifugation. The electrode material obtained using the catalyst has good oxygen electrocatalytic ability, and the starting potential of the oxygen reduction reaction is close to 1.0V.

Description

Technical Field

[0001] The invention relates to a 3D porous spherical carbon shell-supported transition metal single atom catalyst and a preparation method and application thereof, belonging to the technical field of fuel cell electrocatalyst preparation. Background Art

[0002] Fuel cells are an environmentally friendly, efficient new energy source consisting of two half reactions: fuel oxidation at the anode and oxygen reduction at the cathode. The oxygen reduction reaction (ORR) is a very important electrochemical reaction in various renewable energy storage and conversion devices such as fuel cells and metal-air batteries. The oxidation reaction rate is much greater than the reduction reaction rate. Therefore, it is particularly important to increase the oxygen reduction reaction rate at the cathode. However, the cathode reaction kinetics are extremely slow. Currently, commercial precious metal catalysts such as Pt are expensive and structurally unstable, which has become one of the bottlenecks for the large-scale use of fuel cells. Therefore, a low-cost catalyst that can alleviate the sluggish electrocatalytic ORR kinetics and is efficient and stable is very necessary. Summary of the invention

[0003] In order to solve the above-mentioned existing technical problems, the present invention provides a 3D porous spherical carbon shell-supported transition metal single-atom catalyst and a preparation method and application thereof.

[0004] The technical solution of the present invention:

[0005] A 3D porous spherical carbon shell-supported transition metal single atom catalyst is based on an externally functionalized spherical template, a metal organic framework precursor and an organic solvent as raw materials, a double solvent induction method is used to obtain a uniformly dispersed phase, and then vacuum dried and calcined to obtain a 3D porous spherical carbon shell-supported transition metal single atom catalyst.

[0006] Further defined, the preparation method of the externally functionalized spherical template is as follows:

[0007] A spherical template, a functional group source A and an initiator are added to a solvent, reacted at 50°C to 80°C for 10 hours, cooled to room temperature after the reaction, washed once by centrifugation with water and ethanol in sequence, assembled by centrifugation at a high speed, and then dried at 80°C for 12 hours under a vacuum state to obtain an externally functionalized spherical template.

[0008] It is further defined that the spherical template is polystyrene, silicon dioxide or titanium dioxide, and the solvent is methanol or distilled water.

[0009] It is further defined that the functional group supply source A is one or a mixture of two or more of methyl methacrylate, acrylic acid or ammonium bicarbonate in any proportion.

[0010] In a further embodiment, the initiator is potassium persulfate.

[0011] Further defined, the preparation method of the externally functionalized spherical template is as follows:

[0012] The spherical template and functional group source A are added to the solvent, reacted at 50°C-80°C for 10 hours, cooled to room temperature after the reaction, washed once by centrifugation with water and ethanol in sequence, centrifuged at high speed, and dried at 80°C for 12 hours under vacuum to obtain an externally functionalized spherical template.

[0013] In a further embodiment, the spherical template is polystyrene, silicon dioxide or titanium dioxide.

[0014] In a further embodiment, the solvent is methanol or distilled water.

[0015] In a further embodiment, the functional group supply source A is a coupling agent of polyvinyl pyrrolidone.

[0016] The preparation method of the above-mentioned 3D porous spherical carbon shell-supported transition metal single atom catalyst specifically comprises the following steps:

[0017] (1) dispersing the externally functionalized spherical template in a methanol solvent by ultrasonic treatment at a power of 400 W to 2000 W for 30 min to 1 h, adding a metal organic framework precursor and stirring to obtain a mixed solution;

[0018] (2) adding ammonia water to the mixture, reacting for 1 hour, adding polyvinyl pyrrolidone, continuing to react for 1 hour, washing, centrifuging and drying;

[0019] The volume of ammonia added is 1 to 1.5 times the volume of methanol in step (1);

[0020] (3) Finally, calcination is performed to obtain a 3D porous spherical carbon shell-supported transition metal single atom catalyst.

[0021] It is further defined that the metal organic framework precursor includes a metal salt and an organic ligand, and the metal salt is one or two or more of zinc nitrate, cobalt nitrate, iron nitrate or zirconium chloride mixed in any proportion.

[0022] It is further defined that the organic ligand is one or a mixture of two or more of dimethylimidazole, methylimidazole or terephthalic acid in any proportion.

[0023] It is further defined that the mass ratio of the externally functionalized spherical template to the metal organic framework precursor is 1:(1.2-28).

[0024] It is further defined that the mass ratio of the externally functionalized spherical template to the metal organic framework precursor is 1:(1.5-13).

[0025] It is further defined that the mass ratio of the metal salt to the organic ligand is 1:(1-10).

[0026] It is further defined that the mass ratio of the metal salt to the organic ligand is 1:(1-8).

[0027] It is further defined that the mass ratio of the metal salt to the organic ligand is 1:(1-7).

[0028] It is further defined that the concentration of the organic ligand is 40 mmol / L to 90 mmol / L.

[0029] It is further defined that the concentration of the organic ligand is 50 mmol / L to 80 mmol / L.

[0030] It is further defined that the concentration of the organic ligand is 60 mmol / L to 80 mmol / L.

[0031] It is further defined that the K value of polyvinyl pyrrolidone is 12-30.

[0032] It is further defined that the K value of polyvinyl pyrrolidone is 29-30.

[0033] It is further defined that the washing centrifugal assembly treatment conditions are: first centrifugal treatment at a rotation speed of 8000-9000 rad / min for 5-8 minutes, and then centrifugal treatment at a rotation speed of 10000-11000 rad / min for 5-10 minutes.

[0034] It is further defined that the drying conditions are: treatment at 70-80°C under vacuum conditions for 10h-12h.

[0035] It is further defined that the calcination process is: under a nitrogen atmosphere, first calcining at 200°C to 300°C for 1 to 2 hours, and then raising the temperature to 800°C to 900°C for calcining for 1 hour to 2 hours.

[0036] The 3D porous spherical carbon shell-supported transition metal single atom catalyst prepared by the above method is used as a fuel cell ORR catalyst to catalyze the oxygen reduction reaction at the cathode.

[0037] The present invention has the following beneficial effects:

[0038] The present invention mixes a metal organic framework precursor with a spherical template solution coated with a functional group to obtain a 3D spherical metal organic framework precursor solution divided into an outer shell and an inner core structure, and simultaneously obtains a uniformly dispersed 3D spherical metal organic framework through a dual solvent induction technique, and obtains a transition metal single-atom electrocatalyst supported by a carbon shell in a shell-core structure 3D porous spherical shape after centrifugation and heat treatment. The catalyst has good oxygen electrocatalytic ability, an oxygen reduction reaction starting potential of 0.932V, a half-wave potential of 0.82V, and a limiting current density of -5.27mA.

[0039] In addition, the present invention also has the following advantages:

[0040] (1) The present invention uses a dual solvent induction technology to prepare a uniform and completely coated spherical structure transition metal organic framework oxygen electrocatalyst, which not only has excellent ORR performance, but also can be used as a substrate to provide a better mass transfer capacity for loading other metals;

[0041] (2) The spherical template used in the present invention can better anchor metal particles by carboxylic acid functionalization or polyvinyl pyrrolidone modification;

[0042] (3) The present invention subsequently performs a carbonization treatment to effectively increase the graphitization degree and conductivity of the catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 This is a scanning electron microscope photo of the 3D spherical electrocatalyst prepared in Example 1;

[0044] Figure 2 This is a scanning electron microscope photograph of the catalyst prepared in Comparative Example 1;

[0045] Figure 3 This is a scanning electron microscope photograph of the catalyst prepared in Comparative Example 2. DETAILED DESCRIPTION

[0046] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0047] The experimental methods used in the following examples are conventional methods unless otherwise specified. The materials, reagents, methods and instruments used are conventional materials, reagents, methods and instruments in the art unless otherwise specified, and can be obtained through commercial channels by those skilled in the art.

[0048] Embodiment 1:

[0049] (1) Preparation of externally functionalized spherical template (PS-COOH):

[0050] 3.5 ml of styrene, 183 μl of methyl methacrylate, 153 μl of acrylic acid, 131 ml of distilled water (DW) and 0.0816 g of ammonium bicarbonate were mixed, and the mixture was stirred at 50° C. for 1 h. Subsequently, a solution of 78 mg of potassium persulfate dissolved in 10 ml of distilled water was added, and the mixture was stirred at 80° C. for 10 h. After cooling, the mixture was centrifuged and washed once with distilled water at 11000 rad / min, and once with ethanol, and then dried at 80° C. under vacuum for 12 h to obtain a carboxylic acid functionalized polystyrene polymer (PS-COOH) as a template for later use.

[0051] (2) The zinc metal organic framework ZIF-8 is uniformly and independently nucleated on the PS-COOH spheres by a dual solvent induction method:

[0052] 1 g of PS-COOH obtained in the above step (1) was dispersed in 50 ml of methanol solution as the core solution, 0.799 g of dimethylimidazole was added and stirred until completely dissolved, then 0.425 g of zinc nitrate dissolved in 10 ml of methanol was slowly added, 60 ml of saturated ammonia solution was added, and the mixture was stirred and reacted at room temperature for 1 h, 0.018 g of PVP (K=29-30) was added, and the mixture was stirred and reacted at room temperature for 1 h, followed by washing with ethanol at 9000 rad / min for 5 minutes, and then washing with ethanol at 11000 rad / min for 8 minutes.

[0053] (3) Calcination treatment:

[0054] The reaction solution obtained in step (2) was dried under vacuum at 80° C. for 12 h, then calcined under nitrogen atmosphere at 200° C. for 2 h, and then heated to 800° C. for 2 h to obtain a ZIF-8-H oxygen electrocatalyst.

[0055] (3) Structural characterization and performance testing:

[0056] ① The microstructure of the uncalcined PS-loaded zinc metal organic framework ZIF-8 (PS@ZIF-8) was characterized, as shown in the scanning electron microscope photo. Figure 1 As shown by Figure 1 It can be seen that after assembly, a compact, nearly hexagonal catalyst is obtained, and from the spherical part in the lower left corner of Image 1, it can be seen that its morphology is still a 3D spherical catalyst before assembly.

[0057] ② The electrochemical performance of the calcined ZIF-8-H oxygen electrocatalyst was tested:

[0058] The ZIF-8-H oxygen electrocatalyst, 5% naphthalene solution and anhydrous ethanol were mixed and then subjected to ultrasonic dispersion treatment. After coating the electrode, the test results showed that the starting potential of the oxygen reduction reaction was close to 1.0V.

[0059] Comparative Example 1:

[0060] This comparative example does not undergo dual solvent induction:

[0061] (1) Preparation of externally functionalized spherical template (PS-COOH):

[0062] 3.5 ml of styrene, 183 μl of methyl methacrylate, 153 μl of acrylic acid, 131 ml of distilled water (DW) and 0.0816 g of ammonium bicarbonate were mixed, and the mixture was stirred at 50° C. for 1 h. Subsequently, a solution of 78 mg of potassium persulfate dissolved in 10 ml of distilled water was added, and the mixture was stirred at 80° C. for 10 h. After cooling, the mixture was centrifuged and washed once with distilled water at 11000 rad / min, and once with ethanol, and then dried at 80° C. under vacuum for 12 h to obtain a carboxylic acid functionalized polystyrene polymer (PS-COOH) as a template for later use.

[0063] (2) Under the condition that the solvent is distilled water DW, the zinc organic metal framework ZIF-8 is grown on the PS sphere:

[0064] 1 g of PS-COOH obtained in the above step (1) was dispersed in 60 ml of DW as the core solution, 0.799 g of dimethylimidazole was added and stirred until completely dissolved, then 0.425 g of zinc nitrate dissolved in 60 ml of DW was slowly added, and the mixture was stirred and reacted at room temperature for 1 h, 0.018 g of PVP (K=29-30) was added, and the mixture was stirred and reacted at room temperature for 1 h, then the solution was centrifuged at 8000 rad / min for 5 minutes, and the above steps were repeated for a total of three centrifugal washes.

[0065] (3) Calcination treatment:

[0066] The reaction solution obtained in step (2) was dried under vacuum at 80° C. for 12 h, then calcined under nitrogen atmosphere at 200° C. for 2 h, and then heated to 800° C. in two stages for calcination for 2 h to obtain a ZIF-8-H oxygen electrocatalyst.

[0067] (3) Structural characterization and performance testing:

[0068] ① The microstructure of PS@ZIF-8 was characterized, and the scanning electron microscope photos are shown in Figure 2 As shown, by Figure 1 By comparison, although the dispersion is good under the action of PVP, the coated ZIF-8 nucleates and grows independently and unevenly.

[0069] ② The electrochemical performance of the calcined comparative sample ZIF-8-H oxygen electrocatalyst was tested:

[0070] The ZIF-8-H oxygen electrocatalyst, 5% naphthalene solution and anhydrous ethanol were mixed and then subjected to ultrasonic dispersion treatment. After coating the electrode, the test results showed that the starting potential of the oxygen reduction reaction was close to 0.8V.

[0071] Comparative Example 2:

[0072] The spherical template of this comparative example is not functionalized and no dual solvent induction is performed:

[0073] 1) Preparation of spherical template (PS):

[0074] A mixture of 3.5 ml of styrene, 94 μl of oleic acid (emulsifier) ​​and 131 ml of distilled water (DW) was stirred at 50° C. for 1 h, and then a solution of 78 mg of potassium persulfate dissolved in 10 ml of distilled water was added, and stirred at 80° C. for 10 h. After cooling, the mixture was centrifuged and washed once with distilled water at 11000 rad / min, and once with ethanol, and then dried at 80° C. under vacuum for 12 h to obtain a polystyrene polymer PS as a template for later use.

[0075] (2) Under the condition that the solvent is distilled water DW, the zinc organic metal framework ZIF-8 is grown on the PS sphere:

[0076] 1 g of PS obtained in the above step (1) was dispersed in 60 ml of DW as the core solution, 0.799 g of dimethylimidazole was added and stirred until completely dissolved, then 0.425 g of zinc nitrate dissolved in 60 ml of DW was slowly added, and the mixture was stirred and reacted at room temperature for 1 h, 0.018 g of PVP (K=29-30) was added, and the mixture was stirred and reacted at room temperature for 1 h, followed by centrifugation at 8000 rad / min for 5 minutes, and the above steps were repeated for a total of three centrifugal washes.

[0077] (3) Calcination treatment:

[0078] The reaction solution obtained in step (2) was dried under vacuum at 80° C. for 12 h, then calcined under nitrogen atmosphere at 200° C. for 2 h, and then heated to 800° C. in two stages for calcination for 2 h to obtain a ZIF-8-H oxygen electrocatalyst.

[0079] (3) Structural characterization:

[0080] ① The microstructure of PS@ZIF-8 was characterized, and the scanning electron microscope photos are shown in Figure 3 As shown, Figure 2 By comparison, it can be seen that there is no functional group anchoring, so the organic metal framework cannot completely cover the spherical template, and because it is not induced by double solvents, the organic metal framework nucleates and grows independently and unevenly.

Claims

1. A method for preparing a 3D porous spherical carbon shell-supported transition metal single atom catalyst, characterized in that: Using an externally functionalized spherical template as the substrate, a metal organic framework precursor and an organic solvent as the raw materials, a double solvent induction method is used to obtain a uniformly dispersed phase, which is then vacuum dried and calcined to obtain a 3D porous spherical carbon shell-supported transition metal single atom catalyst. The method specifically consists of the following steps: (1) dispersing the externally functionalized spherical template in a methanol solvent by ultrasonic treatment at a power of 400 W to 2000 W for 30 min to 1 h, adding a metal organic framework precursor and stirring to obtain a mixed solution; The metal organic framework precursor described in step (1) comprises a metal salt and an organic ligand, wherein the metal salt is zinc nitrate, the organic ligand is dimethylimidazole, the mass ratio of the externally functionalized spherical template to the metal organic framework precursor is 1:(1.2-28), the molar ratio of the metal salt to the organic ligand is 1:(1-10), and the concentration of the organic ligand is 60 mmol / L-80 mmol / L; (2) adding ammonia water to the mixture, reacting for 1 hour, adding polyvinyl pyrrolidone, continuing to react for 1 hour, washing, centrifuging and drying; The volume of ammonia water added is 1 to 1.5 times the volume of methanol in step (1); the molecular weight K value of the added polyvinyl pyrrolidone is 12 to 30; The centrifugal assembly treatment operation in step (2) is: firstly centrifugation at a speed of 8000-9000 rad / min for 5-8 min, and then centrifugation at a speed of 10000-11000 rad / min for 5-10 min; (3) finally calcining to obtain a 3D porous spherical carbon shell-supported transition metal single atom catalyst; The calcination process in step (3) is as follows: first, in a nitrogen atmosphere, keep the temperature at 200° C. for 2 h, then raise the temperature to 800° C. and calcine for 2 h; The preparation method of the externally functionalized spherical template is as follows: A spherical template, a functional group source A and an initiator are added to a solvent, reacted at 50°C to 80°C for 10 hours, cooled to room temperature after the reaction, washed once by centrifugation with water and ethanol in sequence, assembled by centrifugation at high speed, and then dried at 80°C for 12 hours under vacuum to obtain an externally functionalized spherical template; wherein the spherical template is polystyrene, silicon dioxide or titanium dioxide, the solvent is methanol or distilled water, the functional group source A is one or more of methyl methacrylate, acrylic acid or ammonium bicarbonate mixed in any proportion, and the initiator is potassium persulfate; Or the preparation method of the externally functionalized spherical template is as follows: The spherical template and the functional group source A are added to the solvent, reacted at 50°C to 80°C for 10 hours, cooled to room temperature after the reaction, washed once by centrifugation with water and ethanol in sequence, centrifuged at high speed, and dried at 80°C for 12 hours under vacuum to obtain an externally functionalized spherical template; wherein The spherical template is polystyrene, silicon dioxide or titanium dioxide, the solvent is methanol or distilled water, and the functional group supply source A is a coupling agent of polyvinyl pyrrolidone.

2. The 3D porous spherical carbon shell-supported transition metal single atom catalyst prepared by the method according to claim 1 is used as a fuel cell ORR catalyst to catalyze the oxygen reduction reaction at the cathode.

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