CN108311691B

CN108311691B - Method for synthesizing dodecahedral PtCu nano-frame material by template-free solvothermal method

Info

Publication number: CN108311691B
Application number: CN201810122216.3A
Authority: CN
Inventors: 王爱军; 张小芳; 冯九菊; 黄先燕
Original assignee: Zhejiang Normal University CJNU
Current assignee: Zhejiang Normal University CJNU
Priority date: 2018-02-07
Filing date: 2018-02-07
Publication date: 2020-11-03
Anticipated expiration: 2038-02-07
Also published as: CN108311691A

Abstract

The invention discloses a method for synthesizing a dodecahedron PtCu nano frame material by a template-free solvothermal method, and belongs to the technical field of synthesis of dodecahedron nano frame materials. The technical scheme provided by the invention has the key points that: adding a regulating molecule of hexadecyl trimethyl ammonium chloride into solvent oleylamine, uniformly mixing, stirring, performing ultrasonic treatment, and adding metal precursors of acetylacetone platinum and copper chloride CuCl after completely dissolving₂·2H₂Adding the mixed solution into a reaction kettle, fully reacting for 10 hours at 180 ℃, discharging, washing for a plurality of times by using the mixed solution of ethanol and cyclohexane, and drying to obtain the dodecahedron PtCu nano frame material. The PtCu dodecahedral nano-frame material prepared by the method can obviously improve the catalytic activity of the PtCu dodecahedral nano-frame material on Hydrogen Evolution Reaction (HER) in acidic and alkaline media.

Description

Method for synthesizing dodecahedral PtCu nano-frame material by template-free solvothermal method

Technical Field

The invention belongs to the technical field of synthesis of dodecahedron nano-frame materials, and particularly relates to a method for synthesizing dodecahedron PtCu nano-frames (PtCu DNFs) by a template-free solvothermal method.

Background

A series of problems caused by energy consumption and fossil fuel combustion are receiving wide attention, and the development of renewable green energy is an important strategic route to solve the problems. Pt nanomaterials are known to be the most effective catalysts in many important applications, but Pt catalysts are expensive, slow in reaction kinetics and poor in stability. Therefore, a long-standing problem in preparing nanocatalysts has been how to increase the catalytic activity and metal utilization of Pt-based catalysts.

At present, the solution mainly builds on the following aspects: 1) alloying with transition metal, reducing the use amount of noble metal Pt and simultaneously improving the catalytic performance of the noble metal Pt; 2) the morphology and the structure of the Pt-based catalyst are regulated and controlled, and the catalytic active sites on the surface are improved; 3) and a hollow nano structure in the interior is constructed, so that the utilization efficiency of the noble metal is increased. However, the catalyst tends to aggregate or sinter during the reaction, resulting in a significant decrease in the activity of the catalyst, and therefore, how to improve the stability of the catalyst while ensuring the activity of the catalyst remains a problem to be solved at present. The development and design of the nano-framework material with the highly open three-dimensional structure bring new opportunities for overcoming the problem, and the nano-framework material with the unique structure not only keeps large specific surface area, but also can effectively reduce aggregation and sintering, and improves the catalytic activity and stability of the catalyst.

The synthesis strategies for the nano-frame materials can be divided into two main categories: site-selective deposition and etching, and dealloying of nanocrystals, these voiding mechanisms mainly result from synergistic mechanisms under the multiple actions of displacement reactions, oxidative etching, intra-particle atomic diffusion, or combinations thereof. The synthesis method is mainly designed into a three-dimensional Pt-based alloy nano-frame structure with controllable morphology according to the factors of intermetallic oxidation-reduction potential, metal stability and the like. However, the nano-framework is very easily influenced by element composition, temperature, regulation molecules and a reducing agent in the forming process, so that a novel framework nano-crystal growth regulation system is developed, the element composition, the surface structure, the appearance and the physical size of the nano-framework are regulated to optimize the catalytic performance of the nano-framework, and the application of the nano-framework in energy catalysis is deeply discussed.

Disclosure of Invention

The invention provides a simple and easily realized method for synthesizing a dodecahedral PtCu nano-frame material by a template-free solvothermal method for avoiding the use of templates and etchants in the prior art.

The invention adopts the following technical scheme for solving the technical problems, and the method for synthesizing the dodecahedral PtCu nano frame material by the template-free solvothermal method is characterized by comprising the following specific steps of: adding a regulating molecule of hexadecyl trimethyl ammonium chloride into solvent oleylamine, uniformly mixing, stirring, performing ultrasonic treatment, and adding metal precursors of acetylacetone platinum and copper chloride CuCl after completely dissolving₂·2H₂O and a reducing agent allantoin, wherein the molar concentration of hexadecyltrimethylammonium chloride is 25mM, the molar concentration of platinum acetylacetonate is 2mM, the molar concentration of copper chloride is 2mM, and the molar concentration of allantoin is 25mM, adding the mixed solution into a reaction kettle, fully reacting for 10 hours at 180 ℃, discharging, washing for several times by using the mixed solution of ethanol and cyclohexane, and drying to obtain the dodecahedron PtCu nanometer frame material.

Further preferably, the cube in the prepared PtCu nano-frame material is a uniformly dispersed dodecahedron nano-frame, and the specific process of forming the dodecahedron nano-frame structure is as follows: the method comprises the steps that a metal precursor copper chloride is reduced into Cu atoms, a metal precursor platinum acetylacetonate undergoes a displacement reaction to finally form a PtCu nucleus, the formed PtCu nucleus is selectively precipitated and dissolved along the top and the edge of a {110} crystal face in the presence of a regulating molecule hexadecyl trimethyl ammonium chloride, solid Cu-rich nanocrystals are formed after 2 hours of reaction time, a hollow structure is gradually formed in a solid shape under the displacement action as the time is prolonged to 6 hours, and a hollow intermediate undergoes a bimetallic displacement reaction as the time is prolonged to 10 hours to finally form a dodecahedral framework structure.

Compared with the prior art, the invention has the following advantages: the PtCu DNFs material is prepared by a template-free solvothermal method, the preparation method is simple, and compared with commercial Pt/C and Pt black, the dodecahedral PtCu nano frame material prepared by the method can obviously improve the catalytic activity of the dodecahedral PtCu nano frame material on Hydrogen Evolution Reaction (HER) in acidic and alkaline media.

Drawings

FIG. 1 is a transmission electron microscope image of PtCu DNFs material under different magnifications, wherein the insets in C, D and E are corresponding structural models, and the insets in a and b are Fast Fourier Transform (FFT) images;

FIG. 2 is a schematic diagram of a PtCu DNFs material formation process;

in FIG. 3, A is the polarization curves of PtCu DNFs, Pt/C and Pt black in 0.5M KOH solution, B is the Tafel slope, C is the HER polarization curves before and after 1000 cycles of the test in 0.5M KOH solution saturated with nitrogen and D is-0.05Vvs.Plot of chronoamperometry at NHE potential;

in FIG. 4, A is PtCu DNFs, Pt/C and Pt black at 0.5M H₂SO₄Graph of HER in solution, B is Tafel slope, C is 0.5M H saturated in nitrogen₂SO₄HER polarization curve chart before and after 1000-circle cycle test in solution and D is-0.03Vvs.Chronoamperometric plot at NHE potential.

Detailed Description

The present invention is described in further detail below with reference to examples, but it should not be construed that the scope of the above subject matter of the present invention is limited to the following examples, and that all the technologies realized based on the above subject matter of the present invention belong to the scope of the present invention.

Example 1

Reagent and instrument

Cetyl trimethyl ammonium chloride, platinum acetylacetonate, copper chloride (CuCl)₂·2H₂O), ethanolamine, oleylamine, simethicone, ethanol and cyclohexane were purchased from the Shanghai chemical plant, and all the reagents were analytically pure. Scanning electron microscope (SEM, JSM-6390LV, JEOL, Japan), transmission electron microscope (TEM, JEM-2100, JEOL, Japan) with acceleration voltage of 200kV, Pthe chemical composition of the tCu DNFs materials was determined by energy spectroscopy (EDX, Oxford), X-ray diffraction (XRD).

Adding a regulating molecule of hexadecyl trimethyl ammonium chloride (CTAC 25 mM) into solvent oleylamine (20 mL), uniformly mixing, stirring, performing ultrasonic treatment, and adding metal precursors of platinum acetylacetonate and copper chloride CuCl after the solution is dissolved₂·2H₂O and a reducing agent allantoin, wherein the molar concentration of platinum acetylacetonate is 2mM, the molar concentration of copper chloride is 2mM, and the molar concentration of allantoin is 25mM, adding the mixed solution into a reaction kettle, fully reacting for 10h at 180 ℃, discharging, washing for several times by using the mixed solution of ethanol and cyclohexane, and drying to obtain the dodecahedron PtCu nano frame material.

FIG. 1 is a transmission electron microscopy fast Fourier transform image of PtCu DNFs. As can be seen from the figure, the prepared nano material is composed of uniformly dispersed hollow cubes, a single nano structure shows that the hollow cubes are dodecahedral nano frames, twin crystals exist on the surfaces of the nano frame structures, and the surface activity is favorably improved, so that the catalytic performance of the nano material is enhanced. The fast fourier transform plot of fig. 1 demonstrates its good crystallographic structure.

FIG. 2 shows the growth mechanism of PtCu DNFs, and the formation of the dodecahedral nano-frame structure can be divided into two steps: reduction of precursor copper chloride, and replacement between copper and platinum ions. According to related documents, Cu is reduced earlier than Pt, a metal precursor copper chloride is reduced into Cu atoms, a metal precursor platinum acetylacetonate undergoes a displacement reaction to finally form a PtCu core, the formed PtCu core is selectively precipitated and dissolved along the top and the edge of a {110} crystal face in the presence of a regulatory molecule hexadecyltrimethylammonium chloride, a solid Cu-rich nanocrystal is formed after 2 hours of reaction time, a hollow structure is gradually formed in the solid morphology under the displacement action as the time is prolonged to 6 hours, and a hollow intermediate undergoes a bimetallic displacement reaction as the time is prolonged to 10 hours to finally generate a dodecahedron nano-frame structure.

Fig. 3 shows the catalytic application of PtCu DNFs materials to Hydrogen Evolution Reaction (HER) under alkaline conditions. A in FIG. 3 is a polarization diagram of PtCu DNFs, Pt/C and Pt black in 0.5M KOH solution, the peak-start power of the PtCu DNFsThe position (-25 mV) is more positive than commercial Pt/C (-28 mV) and Pt black (-58 mV), and the Tafel slope (55 mV dec)^–1) Is smaller than that of the control material Pt/C (64 mV dec)^–1) And Pt black (81 mV dec)^–1) This demonstrates that PtCu DNFs catalysts have better catalytic activity towards HER in alkaline media. In FIG. 3, C and D are graphs of HER polarization curves and timing current curves before and after 1000 cycles of cycle test in 0.5M KOH solution saturated with nitrogen, and it can be seen from the graph C that the polarization curves are basically coincident before and after the cycle test, showing the better stability, and in the graph D, the PtCu DNFs material is at-0.05VvsThe current density drop at the NHE potential (16%) was less than that of Pt/C (47.2%) and Pt black (73.8%), which further demonstrates the superior catalytic performance and stability of PtCu DNFs.

FIG. 4 shows the catalytic application of PtCu DNFs to Hydrogen Evolution (HER) under acidic conditions. A in FIG. 4 is PtCu DNFs, Pt/C and Pt black at 0.5M H₂SO₄Polarization profile in solution, PtCu DNFs had a more positive onset (-27 mV) than commercial Pt/C (-32 mV) and Pt black (-63 mV), and Tafel's slope (34 mV dec)^–1) Comparable to Pt/C, but less black than Pt (45 mV dec)^–1) Much smaller, this demonstrates the superior catalytic activity of PtCu DNFs catalysts on HER in acidic media. In FIG. 3C and D are 0.5M H saturated in nitrogen₂SO₄The graphs of HER polarization curves and timing current curves before and after 1000 cycles of cycle test in the solution show that the polarization curves are basically superposed before and after the cycle test, thereby showing better stability, and in the test of the stability of the graph D, the PtCu DNFs material is at-0.03VvsThe current density drop at the NHE potential (8.4%) was less than that of Pt/C (10.3%) and Pt black (44.7%), which further demonstrates the superior catalytic performance and stability of PtCu DNFs materials.

Example 2

In this example, the CTAC concentration of the regulatory molecule was changed (10 mM, 35 mM), and other experimental conditions were kept unchanged with reference to example 1, and the prepared PtCu NPs material was shown in the text that the hollow structure was not complete when the concentration of the regulatory molecule was decreased, and that the agglomeration was severe when the concentration of the regulatory molecule was increased to 35 mM.

Example 3

In this example, 6-aminouracil was used as a reducing agent in place of allantoin, and other experimental conditions were the same as in example 1, and the prepared PtCu NPs material was shown in the support material, and the morphology was no longer a hollow cubic structure.

As can be seen from examples 1-3, control of reaction time, concentration of the controlling molecule (CTAC) and kind of the reducing agent is crucial in the construction of the dodecahedral nano-frame.

The foregoing embodiments illustrate the principles, principal features and advantages of the invention, and it will be understood by those skilled in the art that the invention is not limited to the foregoing embodiments, which are merely illustrative of the principles of the invention, and that various changes and modifications may be made therein without departing from the scope of the principles of the invention.

Claims

1. A method for synthesizing a dodecahedral PtCu nano-frame material by a template-free solvothermal method is characterized by comprising the following specific steps: adding a regulating molecule of hexadecyl trimethyl ammonium chloride into solvent oleylamine, uniformly mixing, stirring, performing ultrasonic treatment, and adding metal precursors of platinum acetylacetonate and CuCl after completely dissolving₂·2H₂O and allantoin as reductant, wherein the molar concentration of hexadecyl trimethyl ammonium chloride is 25mM, the molar concentration of platinum acetylacetonate is 2mM, and CuCl₂·2H₂Adding the mixed solution into a reaction kettle, fully reacting for 10 hours at 180 ℃, discharging, washing for several times by using the mixed solution of ethanol and cyclohexane, and drying to obtain the dodecahedron PtCu nano frame material, wherein the molar concentration of O is 2mM and the molar concentration of allantoin is 25 mM;

the prepared PtCu nanometer frame material consists of uniformly dispersed hollow cubes, the hollow cubes are dodecahedron PtCu nanometer frames, twin crystals exist on the surfaces of the nanometer frame structures, and the specific process of forming the dodecahedron PtCu nanometer frame structures is as follows: metal precursorBulk CuCl₂·2H₂O is reduced into Cu atoms, a metal precursor platinum acetylacetonate undergoes a displacement reaction to finally form a PtCu nucleus, the formed PtCu nucleus is selectively precipitated and dissolved along the top and the edge of a {110} crystal face in the presence of a regulating molecule hexadecyl trimethyl ammonium chloride, a solid Cu-rich nanocrystal is formed after 2 hours of reaction time, a hollow structure is gradually formed in the solid shape under the displacement action as the time is prolonged to 6 hours, and a hollow intermediate undergoes a bimetallic displacement reaction as the time is prolonged to 10 hours to finally form a dodecahedron framework structure.