CN105945298B - A kind of preparation method of hollow palladium nanosphere - Google Patents

Abstract

The invention discloses a method for preparing hollow palladium nanospheres. In the method, polyethyleneimine is used as a stabilizer and ascorbic acid is used as a reducing agent to first synthesize cuprous oxide nanospheres, and then cuprous oxide nanospheres are used as templates, hydrazine hydrate As a reducing agent, potassium chloropalladate or palladium chloride is reduced into hollow palladium nanospheres with regular shape, uniform size, good dispersion and stability by using a hydrothermal reduction method. The preparation method of the invention is simple and economical, and the prepared hollow palladium nanospheres exhibit excellent electrocatalytic activity and stability for the formic acid catalytic reaction, have potential application prospects in the field of direct formic acid fuel cells, and are suitable for large-scale industrial production.

Description

A kind of preparation method of hollow palladium nanosphere

technical field

The invention relates to a method for preparing palladium nanoparticles, in particular to a method for preparing hollow palladium nanospheres. The palladium nanoparticles are used as catalysts to exhibit higher catalytic activity and stability to formic acid.

Background technique

The proton exchange membrane fuel cell (PEMFC) using hydrogen as fuel has not yet been commercialized due to problems such as high price, no suitable hydrogen source, and freezing of the Nafion membrane below 0°C (Design of active Pt on TiO2 based nanofibrous cathode for superior PEMFC performance and durability at high temperature. Applied Catalysis B: Environmental, 2017; 204:421-429). Direct methanol fuel cell (DMFC) has the advantages of convenient fuel storage, transportation and use, small size and high specific energy, but methanol is toxic, volatile, highly flammable, and easily permeates Nafion membrane, causing battery performance to decline. Research in recent years has found that formic acid is a good substitute fuel for methanol, and direct formic acid fuel cells (DFAFC) have many advantages, such as formic acid being non-toxic, non-flammable, etc. (Influence of solution pH on Pt anode catalyst in direct formic acid fuel cells .ACSCatalysis, 2015;5:6848-6851). Due to the repulsion between the sulfonic acid group and the formate anion in the Nafion membrane, the permeability of formic acid to the Nafion membrane is much lower than that of methanol, and DFAFC has received more and more attention (Carbon supported Pd-based bimetallic and trimetallic catalyst for formic acid electrochemical oxidation. Applied Catalysis B: Environnebtal, 2016; 180:758-765).

In DFAFC, the oxidation of formic acid on the palladium catalyst mainly proceeds through the direct route, so the electrocatalytic activity of the palladium catalyst for the oxidation of formic acid is much better than that of the platinum catalyst. Therefore, more and more attention has been paid to palladium catalysts (Pd-Cu alloy with hierarchical network structure as enhanced electrocatalysts for formic acid oxidation. International Journal of Hydrogen Energy, 2016; 41:6773-6780). However, due to the scarcity of palladium reserves, how to reduce the amount of palladium on the premise of improving the activity and selectivity of palladium-based catalysts is still a research hotspot in this field.

According to previous studies, since the particle size, morphology and crystal plane of palladium particles have a great influence on the performance of palladium catalysts, it is very important to design palladium nanostructures with controllable morphology and particle size. For example, the catalytic performance of small-sized palladium nanoparticles composed of {100} crystal faces to formic acid is much better than that of palladium nanoparticles composed of {110} and {111} crystal faces (Multi-Generation Overgrowth Induced Synthesis of Three-Generation Overgrowth Induced Synthesis of Three- Dimensional Highly Branched Palladium Tetrapods and Their Electrocatalytic Activity for Formic Acid Oxidation. Nanoscale, 2014, 6, 2776-2781). At present, palladium nanostructures with different shapes, such as nano-tetrahedron, nano-octahedron, nano-sphere, nano-wire, nano-hollow sphere and nano-cube, have been synthesized by different methods (including template method, seed crystal method, chemical reduction method). , sol-gel method and thermal decomposition method, etc.) (Arginine-Assisted Synthesis and Catalytic Properties of Single Crystalline Palladium Tetrapods. ACS Applied Materials Interfaces, 2014, 6, 22790-22795).

Contents of the invention

The technical problem to be solved by the present invention is to provide a simple and effective hydrothermal reduction method for preparing hollow palladium nanospheres with uniform shape, size and composition.

The technical solution adopted to solve the above technical problems consists of the following steps:

1. Preparation of cuprous oxide nanospheres

Add copper chloride or copper sulfate, polyethyleneimine, and ascorbic acid in distilled water at a molar ratio of 1:1 to 3:1 to 1.5, mix well, and adjust the pH value of the resulting mixture to 10 to 13 with aqueous sodium hydroxide solution. , and stirred at room temperature for 20 to 30 minutes to obtain a cuprous oxide nanosphere solution.

2. Preparation of hollow palladium nanospheres

Adjust the pH value of the aqueous solution of potassium chloropalladate or palladium chloride to 10-13 with 0.5mol/L aqueous sodium hydroxide solution, then add it to the cuprous oxide nanosphere solution, and add hydrazine hydrate, wherein the chloropalladium acid The molar ratio of potassium or palladium chloride, hydrazine hydrate, and cuprous oxide is 1:7~20:1.5~2, the reduction reaction is carried out at 50~80°C for 20~40 minutes, then stirred at room temperature for 16~24 hours, centrifuged and washed and drying to obtain hollow palladium nanospheres.

In the above step 1, preferably the molar ratio of copper chloride or copper sulfate, polyethyleneimine and ascorbic acid is 1:2:1.2, wherein the number average molecular weight of the polyethyleneimine is 300-1200.

In the above step 2, the molar ratio of potassium chloropalladate or palladium chloride, hydrazine hydrate and cuprous oxide is preferably 1:10:1.85.

In the above step 2, it is further preferred to perform the reduction reaction at 60°C for 30 minutes.

The beneficial effects of the present invention are as follows:

1, the present invention adopts a small amount of polyethyleneimine (PEI) as stabilizer and guiding agent, in the process of preparing cuprous oxide nanosphere, PEI is as the stabilizer of cupric chloride, and the N wherein and the cupric chloride The complexation of Cu ²⁺ makes the rate of reduction reaction between cupric chloride and ascorbic acid more moderate, so as to obtain cuprous oxide nanospheres with controllable size and shape, and excess PEI molecules are adsorbed on the surface of cuprous oxide nanospheres; In the process of preparing hollow palladium nanospheres, the PEI adsorbed on the surface of cuprous oxide nanospheres acts as a guide for the growth of palladium on the surface of cuprous oxide, making it easier for palladium to grow on the surface of cuprous oxide nanospheres, while adsorbing on the surface of cuprous oxide The PEI on the surface of the nanospheres acts as a stabilizer of Cu ²⁺ , making the cuprous oxide easily oxidized by oxygen in the air.

2. The present invention uses cuprous oxide nanospheres as a template and sodium chloropalladate as a palladium precursor, and Pd ²⁺ grows directionally on the surface of cuprous oxide nanospheres under the guidance of PEI adsorbed on the surface of cuprous oxide nanospheres , and then cuprous oxide is oxidized by oxygen in the air to Cu ²⁺ ions under the action of PEI, and Cu ²⁺ ions can be removed by washing, and finally hollow palladium nanospheres with uniform shape and size are obtained.

3. The present invention does not require high temperature, long reaction time, and complex pH regulation process, and is simple to operate, with high product yield and good uniformity, and is suitable for large-scale production.

4. Compared with commercial palladium black, the hollow palladium nanospheres prepared by the present invention exhibit excellent electrocatalytic activity and stability for formic acid catalytic reaction, and have potential application prospects in the field of direct formic acid fuel cells.

Description of drawings

Fig. 1 is the SEM picture of the hollow palladium nanosphere prepared in embodiment 1.

Figure 2 is a TEM image of the hollow palladium nanospheres prepared in Example 1.

Figure 3 is a TEM image of the hollow palladium nanospheres prepared in Example 2.

Figure 4 is a TEM image of the hollow palladium nanospheres prepared in Example 3.

Figure 5 is a TEM image of the hollow palladium nanospheres prepared in Example 4.

Figure 6 is a TEM image of the hollow palladium nanospheres prepared in Example 5.

Figure 7 is a TEM image of the hollow palladium nanospheres prepared in Example 6.

Figure 8 is a TEM image of the hollow palladium nanospheres prepared in Example 7.

detailed description

The present invention will be described in further detail below in conjunction with the accompanying drawings and embodiments, but the protection scope of the present invention is not limited to these embodiments.

Example 1

1. Preparation of cuprous oxide nanospheres

Take 1mL of 0.05mol/L _CuCl2 aqueous solution, 0.2mL of 0.5mol/L polyethyleneimine aqueous solution with a number average molecular weight of 600, 0.6mL of 0.1mol/L ascorbic acid aqueous solution, add 10mL of distilled water, stir and mix for 3 minutes, and use 0.5 A mol/L sodium hydroxide aqueous solution was used to adjust the pH value of the obtained mixed solution to 11.5, and stirred at room temperature for 20 minutes to obtain a cuprous oxide nanosphere solution.

2. Preparation of hollow palladium nanospheres

After adjusting 0.45mL of 0.06mol/L potassium chloropalladate aqueous solution to pH 11.5 with 0.5mol/L sodium hydroxide aqueous solution, add it to the cuprous oxide nanosphere solution obtained in step 1, and add 15.5 μL mass fraction It is an 80% aqueous solution of hydrazine hydrate, heated to 60°C in a water bath, subjected to a constant temperature reduction reaction for 30 minutes, then stirred at room temperature for 24 hours, centrifuged with distilled water, washed, and dried at 60°C to obtain hollow palladium nanospheres (see Figures 1 and 2).

Example 2

In Example 1, the copper chloride used is replaced with equimolar copper sulfate, and potassium chloropalladate is replaced with equimolar palladium chloride, and other steps are the same as in Example 1 to obtain hollow palladium nanospheres (see Figure 3 ).

Example 3

In Example 1, 0.2 mL of 0.5 mol/L polyethyleneimine aqueous solution with a number average molecular weight of 600 was replaced with 0.1 mL of 0.5 mol/L polyethyleneimine aqueous solution with a number average molecular weight of 600, and other steps were the same as in Example 1 , to obtain hollow palladium nanospheres (see Figure 4).

Example 4

In Example 1, 0.2mL of 0.5mol/L polyethyleneimine aqueous solution with number average molecular weight of 600 was replaced with 0.3mL of 0.5mol/L number average molecular weight of polyethyleneimine aqueous solution of 600, other steps were the same as in Example 1 , to obtain hollow palladium nanospheres (see Figure 5).

Example 5

In Example 1, 15.5 μL of 80% hydrazine hydrate aqueous solution was replaced with 30 μL of 80% hydrazine hydrate aqueous solution, and other steps were the same as in Example 1 to obtain hollow palladium nanospheres (see Figure 6).

Example 6

In steps 1 and 2 of Example 1, the pH value was adjusted to 13 with 0.5 mol/L aqueous sodium hydroxide solution, and the other steps were the same as in Example 1 to obtain hollow palladium nanospheres (see Figure 7).

Example 7

In step 2 of Example 1, the water bath was heated to 80° C., and the constant temperature reduction reaction was carried out for 20 minutes. The other steps were the same as in Example 1 to obtain hollow palladium nanospheres (see FIG. 8 ).

Claims (5)

1. a preparation method of hollow palladium nanosphere, is characterized in that it is made up of following steps: (1) Preparation of cuprous oxide nanospheres Add copper chloride or copper sulfate, polyethyleneimine, and ascorbic acid in distilled water at a molar ratio of 1:1 to 3:1 to 1.5, mix well, and adjust the pH value of the resulting mixture to 10 to 13 with aqueous sodium hydroxide solution. , stirring at room temperature for 20 to 30 minutes to obtain a cuprous oxide nanosphere solution; (2) Preparation of hollow palladium nanospheres Adjust the pH value of the aqueous solution of potassium chloropalladate or palladium chloride to 10-13 with 0.5mol/L aqueous sodium hydroxide solution, then add it to the cuprous oxide nanosphere solution, and add hydrazine hydrate, wherein the chloropalladium acid The molar ratio of potassium or palladium chloride, hydrazine hydrate, and cuprous oxide is 1:7~20:1.5~2, the reduction reaction is carried out at 50~80°C for 20~40 minutes, then stirred at room temperature for 16~24 hours, centrifuged and washed and drying to obtain hollow palladium nanospheres. 2. the preparation method of hollow palladium nanosphere according to claim 1 is characterized in that: in step (1), the mol ratio of described copper chloride or cupric sulfate, polyethyleneimine, ascorbic acid is 1:2 :1.2. 3. The method for preparing hollow palladium nanospheres according to claim 1 or 2, characterized in that the number average molecular weight of the polyethyleneimine is 300-1200. 4. the preparation method of hollow palladium nanosphere according to claim 1 is characterized in that: in step (2), the mol ratio of described potassium chloropalladate or palladium chloride, hydrazine hydrate, cuprous oxide is 1:10:1.85. 5. The preparation method of hollow palladium nanospheres according to claim 1 or 4, characterized in that: in the step (2), the reduction reaction is carried out at 60° C. for 30 minutes.