CN113782757A

CN113782757A - PtPd alloy nanowire catalyst and preparation method thereof

Info

Publication number: CN113782757A
Application number: CN202111071960.3A
Authority: CN
Inventors: 杨娟; 刘振中; 李毅; 张祥松
Original assignee: Jiangsu University
Current assignee: Jiangsu University
Priority date: 2021-09-14
Filing date: 2021-09-14
Publication date: 2021-12-10

Abstract

The invention relates to a PtPd alloy nanowire catalyst and a preparation method thereof, belonging to the field of new energy nano materials and the technical field of catalysis. Cetyl trimethyl ammonium bromide is added into a water-chloroform two-phase system to form a soft template, and a strong reducing agent sodium borohydride can reduce platinum and palladium precursors coordinated with the soft template, so that the PtPd nanowire network structure with rich defects and high specific surface area is obtained. The prepared nano-wire is in a worm-shaped structure, the average diameter of the nano-wire is 2-3nm, and compared with the synthesis method of other alloy nano-wires, the preparation method of the invention is simple and environment-friendly, and can be used for large-scale preparation.

Description

PtPd alloy nanowire catalyst and preparation method thereof

Technical Field

The invention relates to a PtPd alloy nanowire catalyst and a preparation method thereof, belonging to the field of new energy nano materials and the technical field of catalysis.

Background

Liquid ammonia (NH) has been the subject of recent years₃) The great advantages shown as hydrogen carrier fuel attract more and more clean energy policy trends and the research enthusiasm of researchers, and with the rise of the electrochemical ammonia synthesis technology, the construction of a green ammonia economic circle from ammonia production to ammonia application is a new mode with prospect for energy development and energy and environmental crisis solving in the future. Direct Ammonia Fuel Cells (DAFCs) have attracted widespread attention as an emerging fuel cell technology by both domestic and foreign scholars, however, the DAFC technology on Ammonia Oxidation (AOR) catalysts is currently slow due to slow kinetics and generally requires high Pt loading to achieve the desired reactionRate, and therefore not cost or efficiency, is sufficient to warrant large-scale commercial application of DAFCs. Pt alloy nanomaterials are currently the most efficient AOR catalysts, exhibiting encouraging electrocatalytic performance. For the Pt alloy nano catalyst, the introduction of another metal can cause the change of Pt electronic structure (the increase of d electron vacancy in Pt), the geometric transformation (the reduction of Pt-Pt bond length) and the alleviation of the surface segregation effect, so that the AOR performance of the alloyed Pt alloy nano material is obviously improved.

In order to control various shapes, structures and components of Pt alloy nanoparticles, extensive research has been conducted, and currently prepared Pt alloy nanoparticles having good grain boundaries are mainly in shapes such as spheres, cubes, octahedrons and tetrahedrons. However, conventional platinum alloy multi-metal nanoparticles have great limitations in terms of durability and thermal stability during the catalytic process. They undergo a rapid structural transformation under harmful corrosion catalytic conditions or during high temperature catalysis, resulting in a loss of performance. In consideration of the inherent superior performances of the one-dimensional nano structure such as anisotropic morphology, high flexibility, high specific surface area, high conductivity and the like, atoms at steps, steps and bends of the high-index nano crystal can also be used as additional catalytic active sites, so that the one-dimensional platinum alloy nano structure is an ideal structure for improving the utilization efficiency of platinum and improving the stability of a catalyst. At present, the synthesis methods of one-dimensional platinum alloy nano materials include chemical vapor deposition, physical vapor deposition, solution liquid-solid growth, seed-mediated anisotropic growth, hydrothermal/solvothermal synthesis, template methods and the like. However, the preparation of one-dimensional platinum alloy nanostructures with desired composition is still a difficult point to find a simple, stable and versatile method to synthesize one-dimensional platinum alloy nanostructures due to the combined challenges of inducing anisotropic growth and controlling multi-element composition.

The first principles of Density Functional Theory (DFT) has been studied by the predecessors on the closely arranged planes of Au, Ag, Cu, Pt, Pd, Ni, Ir, Rh, Co, Os, Ru and Re. Pd was found to be an interesting metal among these studied metals, with binding properties and initiation potentials similar to Pt. Therefore, we invented a simple method to prepare PtPd alloy nanowire structures by using a soft template, which exhibit excellent AOR performance under alkaline test conditions. The method is simple and environment-friendly, can well control components and shapes, and is easy to expand to be popularized to the synthesis of other alloy nano materials with one-dimensional structures on a large scale.

Disclosure of Invention

The invention aims to provide a PtPd alloy nanowire catalyst with a one-dimensional structure, which is prepared by a simple process, low cost and an environment-friendly method, has high AOR performance and rich defects, and has a good application prospect in DAFCs. The method is characterized in that: cetyl Trimethyl Ammonium Bromide (CTAB) is added into a water-chloroform two-phase system to form a soft template, and sodium borohydride (NaBH) is a strong reducing agent₄) The Pt and Pd precursors coordinated with the soft template can be reduced, so that the PtPd nanowire network structure with rich defects and high specific surface area can be obtained. The prepared nano-wire is in a worm-shaped structure, the average diameter of the nano-wire is 2-3nm, and compared with other alloy nano-wire synthesis methods, the preparation method is simple and environment-friendly, and can be used for large-scale preparation.

The principle is as follows: in a water-chloroform two-phase system, CTAB is added to form wormlike micelles possibly, the micelles formed in chloroform droplets form an interconnected network-expanded wormlike micelle network, CTAB molecules are positioned on the interface between a chloroform phase and a water pool containing a Pt and Pd compound in the micelles, and the Pt and Pd complex confined in the reversed micelle network is reduced to obtain the PtPd nanowire with a copied micelle network template structure.

In addition, the metal precursor of Pt in the method is potassium chloroplatinate (K)₂PtCl₆) Potassium chloroplatinite (K)₂PtCl₄) And chloroplatinic acid hexahydrate (H)₂PtCl₆.6H₂O), the metal precursor of Pd is palladium chloride (PdCl)₂) Or chloropalladic acid (H)₂PdCl₄) The PtPd alloy nanowire structures with different proportions can be prepared by adjusting the mass ratio of different Pt and Pd before reaction.

The preparation process of the PtPd alloy nanowire comprises the following steps:

1) weighing a certain amount of CTAB, dissolving in chloroform, and stirring to form transparent CTAB dispersion liquid with different concentrations.

2) And adding the prepared metal precursor solutions of Pt and Pd into the transparent CTAB dispersion liquid according to different atomic mass ratios, and stirring to obtain a mixed solution 1.

3) In order to completely transfer the mixed precursor of Pt and Pd to the chloroform phase, deionized water was added to the mixed solution 1, and then stirred at room temperature to obtain a mixed solution 2.

4) Transferring the mixed solution 2 to an ice bath condition, and stirring NaBH₄Is added dropwise to the mixed solution 2 and stirred until the mixed solution 2 becomes gray, indicating the formation of nanowires.

5) The final sample was collected by centrifugation, washed with ethanol and finally dried in a vacuum oven.

In step 1) above, the concentration of the CTAB dispersion is 15-45mM, preferably 40 mM.

In the step 2), the volume ratio of the CTAB dispersion liquid to the metal precursor solution containing Pt and Pd is 1:1, and the metal precursor solutions of Pt and Pd are respectively in different atomic mass ratios of 90: 10-70: 30, preferably 80: 20; the metal precursor solutions of Pt and Pd were each at a concentration of 20 mM.

In the step 3), the volume ratio of the deionized water to the mixed solution 1 is 8: 1, stirring speed is 100-1500 r/min, the preferred stirring speed is 1000r/min, and stirring time is 30 min.

In the above step 4), NaBH₄The volume ratio of the aqueous solution to the mixed solution 2 is 1: 5, NaBH₄Has a concentration of 50 mM; the stirring speed is 1000r/min, and the stirring time is 1 h; NaBH₄The aqueous solution of (2) was previously stored in a refrigerator for 10min before being added dropwise.

In the step 5), the centrifugal speed is 8000rpm, and the centrifugal time is 5 min; washing with ethanol for 3 times, vacuum drying at 60 deg.C for 12 hr.

The synthesis of one-dimensional Pt alloy nano material, such as seed mediated growth, is carried out in the presence of proper reducing agent, stabilizer and solventAnd a shape inducer, so that the formed anisotropic one-dimensional structure is extremely complex and difficult to control₄The reducing agent is composed of interconnected nano particles prepared by a soft template method, and has the advantages of simple process, low cost, environmental protection and batch large-scale production. In addition, the AOR performance can be further improved by controlling the ratio of different substances of Pt and Pd.

Drawings

FIG. 1 is the Pt: pd 80:20 Pt of the sample obtained₈₀Pd₂₀TEM image of nanowires.

FIG. 2 is the Pt: pd 80:20 Pt of the sample obtained₈₀Pd₂₀HR-TEM image of nanowires.

FIG. 3 shows Pt-nanowires and Pt obtained in examples 1 and 2₈₀Pd₂₀-XRD pattern of nanowires combination.

FIG. 4 shows Pt-nanowires and Pt obtained in examples 1 and 2₈₀Pd₂₀-XPS plots of nanowires combinations.

FIG. 5 shows Pt obtained in example 2₈₀Pd₂₀Cyclic voltammograms of nanowires catalysts.

FIG. 6 shows Pt-nanowires and Pt obtained in examples 1 and 2₈₀Pd₂₀Ammonia oxidation cyclic voltammograms of nanowires catalyst and commercial Pt/C (20%).

Detailed Description

The invention is further illustrated by the following examples.

Example 1

A PtPd alloy nanowire catalyst.

The preparation method comprises the following specific steps:

1) 72.90mg of CTAB were weighed out and dissolved in 5ml of chloroform and stirred to form a clear CTAB dispersion with a concentration of 40 mM.

2) 5ml of the prepared Pt metal precursor solution (20mM) was added to the above-mentioned transparent CTAB dispersion, and stirred to obtain a mixed solution 1.

3) In order to completely transfer the Pt precursor to the chloroform phase, 40ml of deionized water was added to the mixed solution 1, and then stirred at 1000r/min at room temperature for 30min to obtain a mixed solution 2.

4) After stirring, the mixed solution 2 was transferred to an ice bath and 10ml of 50mM NaBH was added under stirring at 1000r/min₄Was added dropwise to the above mixed solution 2, and after stirring for 1 hour, the mixed solution 2 became gray, indicating the formation of nanowires.

5) The final sample was collected by centrifugation (8000rpm,5min), washed 3 times with ethanol, and finally dried in a vacuum oven at 60 ℃ for 12 h.

Example 2

The procedure of example 2 was similar to that of example 1 except that in step 2, 4ml of the prepared Pt metal precursor solution (20mM, potassium chloroplatinate) and 1ml of the prepared Pd metal precursor solution (20mM, palladium chloride) were added to the above clear dispersion.

The obtained Pt was subjected to a transmission electron microscope₈₀Pd₂₀-nanowires for topographical characterization.

FIG. 1 shows the preparation of Pt in example 2₈₀Pd₂₀-nanowires TEM image, from which (a) it can be seen that the product prepared by the soft template method has the appearance of a nanowire or nanowire network, and from which (b) it can be seen that there are abundant vermiform nanowires of PtPd alloy, with uniform diameter distribution.

FIG. 2 shows Pt obtained in example 2₈₀Pd₂₀HR-TEM image of nanowires, it can be seen that nanowires are connected to each other, forming a large extended wire network.

FIG. 3 shows Pt-nanowires and Pt obtained in examples 1 and 2₈₀Pd₂₀XRD pattern of the-nanowires combination, from which Pt-nanowire and Pt can be seen₈₀Pd₂₀Nanowines with high crystallinity and typical face-centered cubic structure, Pt when compared to Pt-nanowines₈₀Pd₂₀The diffraction peaks of nanowires are slightly shifted to higher 2 θ values and greater widths, probably due to the substitution of smaller Pd atoms in the latticeSuch that the lattice distance is reduced.

FIG. 4 shows Pt-nanowires and Pt obtained in examples 1 and 2₈₀Pd₂₀-XPS plots of nanowires combinations. From the graph showing a clear comparison of the Pt 4f spectra, it can be seen that Pt 4f_7/2And Pt 4f_5/2The most intense peaks of (a) are all metallic Pt (0), demonstrating that the metallic precursor is fully reduced. Notably, Pt is compared to Pt-nanowires₈₀Pd₂₀The Pt 4f binding energy of the nanowines is shifted negatively, and the electronic structure of the Pt is changed probably due to the introduction of the Pd element.

FIG. 5 shows Pt obtained in example 2₈₀Pd₂₀CV diagram of the nanowires catalyst under argon saturation, electrolyte of 1.0M KOH solution, scanning window of-0.915-0.085V (vs. Ag/Ag Cl), scanning speed of 20 mV/s. As can be seen from the figure, the CV curve under argon saturation shows a distinct hydrogen adsorption peak under-0.80V and a distinct hydrogen desorption peak under-0.84V, indicating Pt₈₀Pd₂₀Nanowines electrodes exhibit potentially superior AOR performance.

FIG. 6 shows Pt-nanowires and Pt obtained in examples 1 and 2₈₀Pd₂₀Ammonia oxidation cyclic voltammograms of nanowires catalyst and commercial Pt/C (20%). The electrolyte is 1.0M KOH +0.1NH saturated by argon₃The solution was scanned over a window of-0.915-0.085V (vs. Ag/Ag Cl) at a rate of 5 mV/s. 0.1M NH₃The solution is composed of 25-28% NH₄OH was mixed with KOH and deionized water. The results show that: prepared Pt-nanowires and Pt₈₀Pd₂₀The initial potentials of the nanowires catalysts were all lower than that of the commercial Pt/C (20 wt%) catalyst, Pt₈₀Pd₂₀The onset potential of nanowines is significantly lower than Pt-nanowines. Of note is Pt₈₀Pd₂₀The nanowires peak current density has approached that of commercial Pt/C (20 wt%) catalysts.

Claims

1. A preparation method of a PtPd alloy nanowire catalyst is characterized by comprising the following specific steps:

1) weighing a certain amount of CTAB, dissolving in chloroform, and stirring to form transparent CTAB dispersion liquid with different concentrations;

2) adding the prepared metal precursor solutions of Pt and Pd into the transparent CTAB dispersion liquid according to different atomic mass ratios, and stirring to obtain a mixed solution 1;

3) in order to completely transfer the mixed precursor of Pt and Pd to a chloroform phase, deionized water is added into the mixed solution 1, and then the mixed solution 2 is obtained by stirring at room temperature;

4) transferring the mixed solution 2 to an ice bath condition, and stirring NaBH₄The aqueous solution of (a) is added dropwise into the mixed solution 2, and stirred until the mixed solution 2 becomes gray, indicating the formation of nanowires;

2. The method for preparing a PtPd alloy nanowire catalyst as recited in claim 1, wherein, in step 1), the concentration of the CTAB dispersion is 15 to 45 mM.

3. The method of preparing a PtPd alloy nanowire catalyst as recited in claim 2, wherein the concentration of the CTAB dispersion is 40 mM.

4. The preparation method of the PtPd alloy nanowire catalyst as claimed in claim 1, wherein in the step 2), the volume ratio of the CTAB dispersion liquid to the metal precursor solution containing Pt and Pd is 1:1, and the atomic-to-mass ratio of the metal precursor solution containing Pt and Pd is 90: 10-70: 30; the concentrations of the Pt and Pd metal precursor solutions are both 20 mM; the metal precursor of the Pt is one of potassium chloroplatinate, potassium chloroplatinate and chloroplatinic acid hexahydrate, and the metal precursor of the Pd is palladium chloride or chloropalladic acid.

5. The method of claim 4, wherein the atomic mass ratio of the Pt to Pd metal precursor solution is 80: 20.

6. The method for preparing the PtPd alloy nanowire catalyst according to claim 1, wherein in step 3), the volume ratio of deionized water to the mixed solution 1 is 8: 1, stirring speed is 100-1500 r/min, and stirring time is 30 min.

7. The method of claim 6, wherein the stirring rate is 1000 r/min.

8. The method of claim 1, wherein in step 4), NaBH is added to the PtPd alloy nanowire catalyst₄The volume ratio of the aqueous solution to the mixed solution 2 is 1: 5, NaBH₄Has a concentration of 50 mM; the stirring speed is 1000r/min, and the stirring time is 1 h; NaBH₄The aqueous solution of (2) was previously stored in a refrigerator for 10min before being added dropwise.

9. The method for preparing the PtPd alloy nanowire catalyst as claimed in claim 1, wherein in the step 5), the centrifugal rotation speed is 8000rpm, and the centrifugal time is 5 min; washing with ethanol for 3 times, vacuum drying at 60 deg.C for 12 hr.