CN104525189A - Polyhedral Pd-Pt alloy nano catalyst and preparation method and application of nano catalyst - Google Patents

Abstract

The invention belongs to the technical field of electrochemical energy, and relates to a polyhedral Pt-Pd alloy nano-catalyst, which uses octaaminosilsesquioxane as a stabilizer and methanol as a reducing agent, and is prepared by a hydrothermal method to obtain consistent appearance and high dispersibility. Good octahedral Pt-Pd nanoalloy catalysts. The invention has the advantages of large active surface area, high catalytic activity, no harsh conditions for reaction, and simple and easy operation, and has great application prospects in direct formic acid fuel cell anode catalysts.

Description

Polyhedral Pd-Pt alloy nanocatalyst, its preparation method and application

technical field

The invention belongs to the technical field of electrochemical energy, and in particular relates to the preparation and application of a polyhedral Pt-Pd alloy nano catalyst.

Background technique

Due to its advantages of high efficiency, high energy density, zero emission, and fast start-up, fuel cells are known as the most promising high-efficiency and clean power generation technology in the 21st century. Due to the problems of low anode catalyst performance, easy poisoning, easy methanol permeation of Nafion membrane, and methanol toxicity in the current research of direct methanol fuel cells, direct formic acid fuel cells have attracted extensive attention as a substitute for direct methanol fuel cells. Among them, the anode catalyst based on Pt and Pt-based metals is one of the most important key materials for direct formic acid fuel cells. However, platinum-based noble metal catalysts have limitations such as high cost and limited platinum resources, which have become important factors restricting the development and commercialization of direct formic acid fuel cell technology. Therefore, reducing the usage of precious metals, improving the catalytic activity and stability of catalysts, and effectively reducing the manufacturing cost of batteries has become a very meaningful work.

The way of introducing another one or two metals and Pt alloy is an important way to improve the catalytic activity of the catalyst and reduce the cost of the catalyst. In the periodic table of elements, compared with other elements around Pt in the table, since Pd and Pt have the same surface phase cubic structure and relatively close theoretical lattice constants, Pd is the best choice for alloying with Pt. Theoretically, under appropriate conditions, Pt and Pd can be alloyed with any composition. So far, researchers have reported many methods for preparing Pt-Pd alloy nanocatalysts, such as co-reduction method, "seed" mediated growth method, and electrochemical displacement method. In the synthesis of nanomaterials, in addition to the metal components, the morphology of nanocatalysts is also an important factor affecting the catalytic performance. So far, Pt-Pd nanoparticles with various morphologies have been reported for formic acid oxidation or oxygen reduction, including hollow spheres, nanoflowers, nanodendrites, concave structures, cubes, and octahedrons, etc.

Further studies have shown that in the synthesis of nanomaterials, the type and amount of coating agent are important factors affecting the morphology of nanomaterials. In the liquid-phase synthesis of metal nanomaterials, the coating agent or surfactant can interact with the metal surface, thereby changing the free energy of different crystal planes, and then affecting the relative growth rate of different crystal planes. Such changes may lead to different shapes of nanomaterials.

Contents of the invention

Technical problem: the technical problem solved by the present invention is to provide a polyhedral Pt-Pd alloy catalyst with large active surface area, high catalytic activity, no harsh conditions for reaction, and easy operation, and at the same time provide its preparation method and Applications in efficient electrocatalysis of formic acid.

Technical scheme: the method for preparing polyhedral Pt-Pd alloy nano-catalyst of the present invention, comprises the following steps:

(1) Preparation of raw material solution: Dissolve chloroplatinic acid and palladium chloride solids in a dispersion solvent mixed with methanol and water according to the platinum-palladium molar ratio of 1: 1-9; The molar ratio of silsesquioxane is 1:1~5. Add the stabilizer octaaminosilsesquioxane to the above solution, adjust the pH value of the mixture to 3~7 after ultrasonic oscillation, keep stirring The stabilizer is fully contacted and complexed with Pd ions and Pt ions to obtain an active metal precursor mixed solution, wherein the molar number of the metal precursor is the sum of the molar numbers of palladium chloride and chloroplatinic acid;

(2) Reducing the precursor: transfer the active metal precursor mixture prepared in the step (1) to a hydrothermal reaction kettle, the reaction temperature is 90~170°C, and the reaction time is 5~10h;

(3) Post-processing of the product: the solid matter in the product of the step (2) is separated from the liquid, washed with water and ethanol several times, and heated and dried in a vacuum drying oven at 50-90°C to obtain polyhedral Pt -Pd alloy nano catalyst;

In a preferred version of the method of the present invention, the water in steps (1) and (2) is ultrapure water.

In the preferred solution of the method of the present invention, the volume ratio of water and methanol in the dispersion solvent in step (1) is 1:1~6.

In a preferred version of the method of the present invention, hydrochloric acid or sodium hydroxide is used to adjust the pH value in step (1).

The polyhedral Pt-Pd alloy nano-catalyst of the present invention is that metal Pd, metal Pt and stabilizer octaaminosilsesquioxane are complexed into an active metal precursor mixed solution, and then the solid product is dried after reduction and solid-liquid separation. After drying, the molar ratio of the metal Pt to the metal Pd is 1:1-9.

In the preferred solution of the polyhedral Pt-Pd alloy nanocatalyst of the present invention, the molar ratio of the metal precursor to octaaminosilsesquioxane is 1:1-5.

In the preferred solution of the polyhedral Pt-Pd alloy nanocatalyst of the present invention, the catalyst is prepared according to the above method.

The invention also includes the application of the polyhedral Pt-Pd alloy nano-catalyst in formic acid high-efficiency electrocatalysis.

The invention uses octahedral silsesquioxane as a stabilizer and methanol as a reducing agent to prepare an octahedral Pt-Pd nano-alloy catalyst with uniform appearance and good dispersibility through a hydrothermal method, and the catalyst has a polyhedron appearance. The catalyst of the invention has great application prospect in the direct formic acid fuel cell anode catalyst.

Beneficial effect: compared with the prior art, the present invention has the following advantages:

(1) Direct formic acid fuel cell solves the problems of low anode catalyst performance, easy poisoning, easy permeation of methanol through Nafion membrane, and poisonous methanol in direct methanol fuel cell.

(2) Introduce another method of one or two metals and Pt alloys to reduce the usage of precious metals and effectively reduce the manufacturing cost of batteries.

Polyhedral nano-Pt-Pd alloy catalyst provided by the present invention, and traditional carbon-supported Pt-Pd catalyst (Arenz,, Physical Chemistry Chemical Physics, 2003; Li, Electrochimica Acta, 2006; Feng, Catalysis Communications, 2011) and other forms Compared with the surface Pt-Pd alloy catalyst (Liu, J. Power Sources, 2009), in the process of catalyzing the oxidation of formic acid, the polyhedral nano-Pt-Pd alloy catalyst has a lower oxidation potential, so formic acid is more easily oxidized on its surface , and the catalytic performance is stable and long-lasting. In the present invention, octaaminosilsesquioxane is firstly used as the morphology regulator of the Pt-Pd alloy catalyst, and octaaminosilsesquioxane is a novel organic/inorganic hybrid material, and its nanoscale cage skeleton can Effectively combining and utilizing the advantages of hybrid materials to endow materials with better performance has become an important means of preparing high-performance materials. Naka (Nano Letters, 2002) and Letant (Journal of Physical Chemistry C, 2009) have reported the preparation of Pd nanospheres by octaaminosilsesquioxane as a stabilizer, but it is used as a shape regulator for Pt-Pd alloy catalysts. This is the first time. Octaaminosilsesquioxane can be used as a morphology regulator to simplify the preparation process of nanomaterials; in addition, after preparation, compared with other polymer complexing agents, octaaminosilsesquioxane can be removed by high-speed centrifugation, Does not affect the catalytic performance of the catalyst.

Description of drawings

1 is an electron microscope picture of polyhedral Pt1Pd9 alloy nanoparticles in Example 1.

Fig. 2 is the cyclic voltammetry curve of polyhedral Pt1Pd9 alloy nanoparticles in Example 1 in 0.5MH ₂ SO ₄ +0.5MHCOOH solution.

3 is an electron microscope picture of polyhedral Pt3Pd7 alloy nanoparticles in Example 2.

4 is a cyclic voltammetry curve of polyhedral Pt3Pd7 alloy nanoparticles in Example 2 in 0.5MH ₂ SO ₄ +0.5MHCOOH solution.

5 is an electron microscope picture of polyhedral Pt5Pd5 alloy nanoparticles in Example 3.

FIG. 6 is a cyclic voltammetry curve of polyhedral Pt5Pd5 alloy nanoparticles in Example 3 in 0.5MH ₂ SO ₄ +0.5MHCOOH solution.

Detailed ways

The technical solution of the invention will be described in detail below through examples.

The preparation of embodiment 1, Pt1Pd9 alloy

Get 5.2mg of chloroplatinic acid solid and 15.9mg of palladium chloride solid (the ratio of platinum to palladium is 1:9) and dissolve in the mixed solution of methanol and water (the volume ratio of methanol to water is 1:1); 117.3mg octaaminosilsesquioxane (the mol ratio of metal precursor and octaaminosilsesquioxane is 1: 1), use 1mol/L hydrochloric acid solution to regulate the pH value of above-mentioned mixed solution to 5 after ultrasonic oscillation, keep Stirring is the full contact and complexation of the stabilizer with Pd ions and Pt ions to obtain the active metal precursor mixed solution; the prepared raw material solution is transferred to a hydrothermal reactor, the reaction temperature is 90-170 °C, and the reaction time is 10 h; The reduced nanomaterials are separated from the liquid, washed with water and ethanol several times, and heated and dried in a vacuum oven at 50-90°C to prepare polyhedral Pt1Pd9 alloy nanocatalysts.

Disperse a certain amount of PtPd alloy in ultrapure water, take 10ul sample and drop it on the glassy carbon electrode with a diameter of 3mm. After it is completely dried at room temperature, remove 2ul of Nafion solution and evenly coat the surface of the catalyst. After drying at room temperature It can be used as a working electrode.

Taking Example 1 as an example to observe the effect of polyhedral PtPd alloy on efficient catalysis of formic acid as shown in Figure 1 and Figure 2 .

Embodiment 2, the preparation of Pt3Pd7 alloy

Get 15.5mg of chloroplatinic acid solid and 12.5mg of palladium chloride solid (the ratio of platinum to palladium is 3:7) and dissolve in the mixed solution of methanol and water (the volume ratio of methanol to water is 3:1); 234.6mg octaaminosilsesquioxane (the mol ratio of metal precursor and octaaminosilsesquioxane is 1: 5), use 1mol/L hydrochloric acid solution to regulate the pH value of above-mentioned mixed solution to 3 after ultrasonic oscillation, keep Stir to fully contact and complex the stabilizer with Pd ions and Pt ions to obtain a mixed solution of active metal precursor; transfer the prepared raw material solution to a hydrothermal reactor, the reaction temperature is 90-170 ° C, and the reaction time is 6 h; The reduced nanomaterials are separated from the liquid, washed with water and ethanol several times, and heated and dried in a vacuum oven at 50-90°C to prepare polyhedral Pt3Pd7 alloy nanocatalysts.

Taking Example 2 as an example to observe the effect of polyhedral PtPd alloy on formic acid high-efficiency catalysis as shown in Figure 3 and Figure 4, the preparation method of the loaded electrode is the same as that of Example 1.

The preparation of embodiment 3, Pt5Pd5 alloy

Get 25.9mg of chloroplatinic acid solid and 8.9mg of palladium chloride solid (the ratio of platinum to palladium is 5:5) and dissolve in the mixed solution of methanol and water (the volume ratio of methanol to water is 6:1); 234.6mg octaaminosilsesquioxane (the mol ratio of metal precursor and octaaminosilsesquioxane is 1: 2), use 1mol/L hydrochloric acid solution to regulate the pH value of above-mentioned mixed solution to 7 after ultrasonic oscillation, keep Stir to make the stabilizer fully contact and complex with Pd ions and Pt ions to obtain the active metal precursor mixed liquid; transfer the prepared raw material liquid to a hydrothermal reaction kettle, the reaction temperature is 90-170 ° C, and the reaction time is 5 h; The reduced nanomaterials are separated from the liquid, washed with water and ethanol several times, and heated and dried in a vacuum oven at 50-90°C to prepare polyhedral Pt5Pd5 alloy nanocatalysts.

Taking Example 3 as an example to observe the effect of the polyhedral PtPd alloy on efficient catalysis of formic acid, as shown in Figures 5 and 6, the preparation method of the loaded electrode is the same as that of Example 1.

The foregoing embodiments are only preferred implementations of the present invention. It should be pointed out that those skilled in the art can make several improvements and equivalent replacements without departing from the principle of the present invention. Technical solutions requiring improvement and equivalent replacement all fall within the protection scope of the present invention.

Claims (8)

1. a method for preparing polyhedral Pt-Pd alloy nano-catalyst: it is characterized in that, the method may further comprise the steps: (1) Prepare raw material solution: Dissolve chloroplatinic acid and palladium chloride solids in a dispersion solvent mixed with methanol and water according to the molar ratio of platinum to palladium in the ratio of 1:1 to 9; The molar ratio of silsesquioxane is 1:1~5. Add the stabilizer octaaminosilsesquioxane to the above solution, adjust the pH value of the mixture to 3~7 after ultrasonic oscillation, keep stirring The stabilizer is fully contacted and complexed with Pd ions and Pt ions to obtain a mixed solution of active metal precursors; (2) Reducing the precursor: transfer the active metal precursor mixture prepared in the step (1) to a hydrothermal reaction kettle, the reaction temperature is 90~170°C, and the reaction time is 5~10h; (3) Post-processing of the product: the solid matter in the product of the step (2) is separated from the liquid, washed with water and ethanol several times, and heated and dried in a vacuum drying oven at 50-90°C to obtain polyhedral Pt -Pd alloy nano catalyst. 2. The method for preparing polyhedral Pt-Pd alloy nanocatalysts according to claim 1, characterized in that: the water in the steps (1) and (2) is ultrapure water. 3. The method for preparing polyhedral Pt-Pd alloy nanocatalysts according to claim 1 or 2, characterized in that: the volume ratio of water and methanol in the step (1) dispersing solvent is 1:1~6. 4. The method for preparing polyhedral Pt-Pd alloy nanocatalysts according to claim 1 or 2, characterized in that: in the step (1), hydrochloric acid or sodium hydroxide is used to adjust the pH value. 5. A polyhedral Pt-Pd alloy nanocatalyst, is characterized in that: this catalyst is that metal Pd, metal Pt and stabilizing agent octaaminosilsesquioxane are complexed into active metal precursor mixed solution, then through reduction, solidification It is obtained by separating the liquid from the liquid and drying the solid product, and the molar ratio of the metal Pt to the metal Pd is 1:1-9. 6. The polyhedral Pt-Pd alloy nanocatalyst according to claim 5, characterized in that the molar ratio of the metal precursor to octaaminosilsesquioxane is 1:1-5. 7. as claimed in claim: 5 or 6 described polyhedral Pt-Pd alloy nano-catalysts, it is characterized in that: this catalyst is prepared according to the method described in claim 1,2,3 or 4. 8. The application of the polyhedral Pt-Pd alloy nano-catalyst of claim 5, 6 or 7 in the efficient electrocatalysis of formic acid.