CN103165914B - Pt/Au/PdCo/C catalyst, and preparation and application thereof - Google Patents

Abstract

A Pt/Au/PdCo/C catalyst. The catalyst preparation includes (1) preparation of alloyed PdCo/C and (2) preparation of Pt/Au/PdCo/C catalyst. The catalyst has the advantages of low Pt loading and high electrochemical stability, and can be used as a cathode oxygen reduction catalyst for metal-air fuel cells, proton exchange membrane fuel cells, and direct liquid fuel cells.

Description

A kind of Pt/Au/PdCo/C catalyst and its preparation and application

technical field

The invention relates to an oxygen reduction catalyst, in particular to the preparation and application of an oxygen reduction catalyst for a metal-air fuel cell, an oxygen reduction catalyst for a proton exchange membrane fuel cell, and an oxygen reduction catalyst for a direct liquid fuel cell.

Background technique

With the increasing consumption of fuels such as coal, oil and natural gas and the depletion of energy resources, it is urgent to find energy technologies that are environmentally friendly and sustainable. Because of its high energy conversion efficiency, no pollution, no noise and other advantages, fuel cells have become a research hotspot all over the world.

At present, the most effective catalysts for fuel cell cathode ORR catalysts are still Pt and its alloy catalysts. However, the limited reserves and high price of Pt have become one of the obstacles to the commercialization of fuel cells. How to increase the utilization of catalysts without reducing their activity has become a research hotspot recently.

Adzic's research group found that a single layer of Cu atoms was formed on the surface of noble metal particles through Cu-UPD, and then replaced with Pt ²⁺ to obtain a Pt single layer catalyst, in which noble metals such as Pd, Au and their alloys were generally used as the inner core. The highly dispersed Pt greatly improves the ORR specific mass activity of this type of catalyst. However, there are few studies on the stability of such catalysts in electrochemical environments.

The accelerated aging test was carried out on Pt/PdCo/C catalyst, and the CV scan was performed at a scan rate of 100mV s ^-1 in the potential range of 0.6-1.0V vs. NHE, and the half-wave potential of the ORR polarization curve shifted negatively by 34mV after 10k cycles , the catalytic activity was obviously attenuated, indicating that the highly dispersed Pt monolayer on the surface of the catalyst had poor electrochemical stability. Au nanoparticles have good electrochemical stability, and their introduction into electrocatalysts can greatly improve the stability of electrocatalysts. However, the ORR catalytic activity of Au itself is poor, and if it is introduced into the catalyst to cover the active sites of Pt, the catalytic activity may decrease. To this end, we designed a Cu-UPD-replacement method to introduce Au as a sub-monolayer between the surface Pt layer and the PdCo core, aiming at improving the electrochemical stability of the Pt monolayer catalyst without reducing the catalytic activity of ORR. .

Contents of the invention

Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a preparation and application of an oxygen reduction catalyst for a metal-air fuel cell, an oxygen reduction catalyst for a proton exchange membrane fuel cell, and an oxygen reduction catalyst for a direct liquid fuel cell.

In order to achieve the above object, the present invention adopts the following specific solutions to achieve:

A Pt/Au/PdCo/C catalyst, Pt is distributed on the surface of nanoparticles, and Au is located between the Pt shell and the PdCo core. The metal mass in the catalyst accounts for 12-46% of the total mass; wherein the molar ratio of Pd and Co is 5:1-1:1; the molar ratio of Pd and Au is 5:1-12:1; the molar ratio of Pd and Pt It is 10:1-20:1.

The preparation method of described catalyst comprises the following steps,

(1) Preparation of Alloyed PdCo/C

a. Add PdCl ₂ and/or Pd(NO ₃ ) ₂ to deionized water, and at the same time add one or more of Co(NO ₃ ) ₂ , CoCl ₂ , CoBr ₂ , CoSO ₄ , Co(COOH) ₂ , form a mixture, stir to make it evenly mixed, then add carbon carrier to the mixed liquid, and ultrasonically disperse until the mixed liquid is uniform;

b. Add sodium citrate aqueous solution dropwise in the mixed solution obtained in the above step (1) a, and add dropwise NaBH _aqueous solution under the condition of rapid stirring, filter to obtain solid matter after standing, and then use deionized water to obtain The solid matter is washed, and the obtained matter after washing is placed in a vacuum oven to dry to obtain PdCo/C;

c. heat-treating the PdCo/C obtained in step (1)b in a mixture of hydrogen and an inert gas to obtain alloyed PdCo/C;

(2) Preparation of Pt/Au/PdCo/C catalyst

a. In ethanol, add the alloyed PdCo/C obtained in the above step (1) c, stir to make it evenly mixed, then add Nafion emulsion, and ultrasonically disperse until the mixture is uniform;

b. pipette the mixed solution obtained in the above step (2) a, and apply it to the surface of the glassy carbon electrode as a working electrode, and the counter electrode and the reference electrode are respectively Pt wire and a saturated calomel electrode;

c. Place the working electrode obtained in the above step (2)b in the mixed solution of H ₂ SO ₄ and CuSO ₄ and maintain it at a deposition potential of 350-520mV for 1-300s, then quickly immerse the electrode in H ₂ SO ₄ and HAuCl ₄ Put it in the mixed solution and let it stand for 1-10min to carry out the replacement reaction, and then clean the electrode with deionized water;

d. Place the working electrode obtained in the above step (2)c in the mixed solution of H ₂ SO ₄ and CuSO ₄ at a deposition potential of 350-520mV for 1-300s, then quickly immerse the electrode in H ₂ SO ₄ and K ₂ PtCl ₄ Put it in the mixed solution and let it stand for 1-10min to carry out the replacement reaction, and then clean the electrode with deionized water to obtain the Pt/Au/PdCo/C catalyst.

The molar ratio of Pd ²⁺ and Co ²⁺ in the mixture in step (1)a is 5:1-1:1; the concentration of Pd ²⁺ in the mixture is 10-100mmol L ^-1 .

The metal mass in the alloyed PdCo/C in step (1) accounts for 10-40% of the total mass.

The concentration of the sodium citrate aqueous solution in step (1)b is 10-50mmol L ^-1 , and the dosage is 10-50mL; the concentration of the NaBH ₄ aqueous solution is 10-100mmol L ^-1 , and the dosage is 10-50mL; The vacuum drying time is 5-20 hours.

The inert atmosphere described in the step (1) c is a mixture of one or more of argon, helium, nitrogen; the hydrogen volume accounts for 1-10% of the total gas volume; the heat treatment temperature is 200- 600°C, the heat treatment time is 1-3 hours;

The concentration of PdCo/C in ethanol in step (2)a is 0.5-5 mg mL ^-1 ; the mass ratio of Nafion to PdCo/C is 1:10-1:1.

The mass ratio of _H2SO4 and _CuSO4 in the mixed solution of step (2 ₎ c and step (2)d is 5:1-1: ₂ ; the mixed solution of _H2SO4 and _HAuCl4 The mass ratio of the two in the _H2SO4 and _K2PtCl4 mixed solution is 100:1-20:1; the mass ratio of the two in the _H2SO4 and _K2PtCl4 mixed solution is 100:1-20:1; the _H2SO The substance concentration of ₄ is 20-100mmol L ^-1 .

The carbon carrier is: one or a mixture of two or more of XC-72R, BP2000, acetylene black, carbon nanotubes, and graphite;

The Pt/Au/PdCo/C catalyst can be used as an oxygen reduction catalyst for a metal-air fuel cell, an oxygen reduction catalyst for a proton exchange membrane fuel cell, or an oxygen reduction catalyst for a direct liquid fuel cell.

Compared with the prior art, the novel Pt/Au/PdCo/C catalyst of the present invention has the following advantages:

1. The noble metal Pt is distributed on the surface of the nanoparticles, which reduces the loading of Pt, thereby reducing the cost of the catalyst

2. The introduction of Au with good electrochemical stability between the Pt shell and the PdCo core greatly improves the ORR activity and electrochemical stability of the Pt monolayer catalyst.

Description of drawings

Fig. 1 is the stripping curve (according to embodiment 1-5) of Cu deposited under different underpotentials;

Fig. 2 is the stripping curve (according to embodiment 3 and 6-8) of the Cu of underpotential deposition through different time;

Fig. 3 is the cyclic voltammetry (CV) curve and the oxygen reduction reaction (ORR) polarization curve of the sample prepared according to embodiment 1 and comparative example 3 in _0.1M HClO solution;

Fig. 4 is the CV curve and the ORR polarization curve of the sample prepared according to embodiment 1 and comparative example 3 before and after the stability test in 0.1M _HClO solution;

Fig. 5 is the TEM photo before and after the stability test of the sample prepared according to embodiment 1 and comparative example 3 in 0.1M _HClO solution;

FIG. 6 is a TEM photo of the samples prepared according to Example 1 and Comparative Example 2 before and after the stability test in 0.1M HClO ₄ solution.

Detailed ways:

Below in conjunction with embodiment the present invention is described in detail. Of course, the present invention is not limited to these specific examples.

Example 1:

Weigh 28.2mg PdCl ₂ and 9.6mg Co(NO ₃ ) ₂ (Pd/Co atomic ratio is 3:1) and dissolve in 100mL deionized water, add 80mg Vulcan XC-72 carbon powder and ultrasonically disperse for 30min. After uniform dispersion, 25mL of 25mmol L ^-1 sodium citrate aqueous solution was added dropwise, and then 25mL of 80mmol L ^-1 NaBH ₄ solution was slowly added dropwise under rapid stirring. After 30 minutes, the obtained product was filtered, washed with a large amount of deionized water, and dried in a vacuum oven at 80° C. for 8 hours to obtain a PdCo/C catalyst. The alloyed PdCo/C catalyst can be obtained by heat-treating the PdCo/C catalyst at 400° C. for 2 hours under a 5vol% H ₂ /Ar atmosphere.

Disperse 5 mg of alloyed PdCo/C catalyst in 2 mL of ethanol, and add 30 μL of 5% Nafion emulsion as a binder. After ultrasonic dispersion for 15 min, 20 μL of the slurry was pipetted and coated on the surface of a glassy carbon electrode as a working electrode. The working electrode was placed in a mixed solution of 50mmol L ^-1 H ₂ SO ₄ and 50mmol L ^-1 CuSO ₄ for Cu underpotential deposition: first, the deposition potential of 350mV was maintained for 120s to make Cu underpotential deposition on the surface of PdCo nanoparticles, and then Quickly immerse the electrode in the mixed solution of 50mmolL ^-1 H ₂ SO ₄ and 1mmol L ^-1 HAuCl ₄ , let it stand for 4min to make the replacement reaction between Au ³⁺ and Cu ²⁺ , and then clean the surface of the electrode with deionized water. The underpotential deposition of Cu was repeated, and then the electrode was quickly placed in the mixed solution of 50mmol L ^-1 H ₂ SO ₄ and 1mmol L ^-1 K ₂ PtCl ₄ , and stood for 4min to allow the substitution reaction between Pt ²⁺ and Cu ²⁺ , Then the electrode is cleaned with deionized water to obtain the Pt/Au/PdCo/C catalyst.

Example 2:

Weigh 28.2mg PdCl ₂ and 9.6mg Co(NO ₃ ) ₂ (Pd/Co atomic ratio is 3:1) and dissolve in 100mL deionized water, add 80mg Vulcan XC-72 carbon powder and ultrasonically disperse for 30min. After uniform dispersion, 25mL of 25mmol L ^-1 sodium citrate aqueous solution was added dropwise, and then 25mL of 80mmol L ^-1 NaBH ₄ solution was slowly added dropwise under rapid stirring. After 30 minutes, the obtained product was filtered, washed with a large amount of deionized water, and dried in a vacuum oven at 80° C. for 8 hours to obtain a PdCo/C catalyst. The alloyed PdCo/C catalyst can be obtained by heat-treating the PdCo/C catalyst at 400° C. for 2 hours under a 5vol% H ₂ /Ar atmosphere.

Disperse 5 mg of alloyed PdCo/C catalyst in 2 mL of ethanol, and add 30 μL of 5% Nafion emulsion as a binder. After ultrasonic dispersion for 15 min, 20 μL of the slurry was pipetted and coated on the surface of a glassy carbon electrode as a working electrode. The working electrode was placed in a mixed solution of 50mmol L ^-1 H ₂ SO ₄ and 50mmol L ^-1 CuSO ₄ for Cu underpotential deposition: first, the deposition potential of 370mV was maintained for 120s to make Cu underpotential deposition on the surface of PdCo nanoparticles, and then Quickly immerse the electrode in the mixed solution of 50mmolL ^-1 H ₂ SO ₄ and 1mmol L ^-1 HAuCl ₄ , let it stand for 4min to make the replacement reaction between Au ³⁺ and Cu ²⁺ , and then clean the surface of the electrode with deionized water. The underpotential deposition of Cu was repeated, and then the electrode was quickly placed in the mixed solution of 50mmol L ^-1 H ₂ SO ₄ and 1mmol L ^-1 K ₂ PtCl ₄ , and stood for 4min to allow the substitution reaction between Pt ²⁺ and Cu ²⁺ , Then the electrode is cleaned with deionized water to obtain the Pt/Au/PdCo/C catalyst.

Example 3:

Weigh 28.2mg PdCl ₂ and 9.6mg Co(NO ₃ ) ₂ (Pd/Co atomic ratio is 3:1) and dissolve in 100mL deionized water, add 80mg Vulcan XC-72 carbon powder and ultrasonically disperse for 30min. After uniform dispersion, 25mL of 25mmol L ^-1 sodium citrate aqueous solution was added dropwise, and then 25mL of 80mmol L ^-1 NaBH ₄ solution was slowly added dropwise under rapid stirring. After 30 minutes, the obtained product was filtered, washed with a large amount of deionized water, and dried in a vacuum oven at 80° C. for 8 hours to obtain a PdCo/C catalyst. The alloyed PdCo/C catalyst can be obtained by heat-treating the PdCo/C catalyst at 400° C. for 2 hours under a 5vol% H ₂ /Ar atmosphere.

Disperse 5 mg of alloyed PdCo/C catalyst in 2 mL of ethanol, and add 30 μL of 5% Nafion emulsion as a binder. After ultrasonic dispersion for 15 min, 20 μL of the slurry was pipetted and coated on the surface of a glassy carbon electrode as a working electrode. The working electrode was placed in a mixed solution of 50mmol L ^-1 H ₂ SO ₄ and 50mmol L ^-1 CuSO ₄ for Cu underpotential deposition: first, the deposition potential of 390mV was maintained for 120s to make Cu underpotential deposition on the surface of PdCo nanoparticles, and then Quickly immerse the electrode in the mixed solution of 50mmolL ^-1 H ₂ SO ₄ and 1mmol L ^-1 HAuCl ₄ , let it stand for 4min to make the replacement reaction between Au ³⁺ and Cu ²⁺ , and then clean the surface of the electrode with deionized water. The underpotential deposition of Cu was repeated, and then the electrode was quickly placed in the mixed solution of 50mmol L ^-1 H ₂ SO ₄ and 1mmol L ^-1 K ₂ PtCl ₄ , and stood for 4min to allow the substitution reaction between Pt ²⁺ and Cu ²⁺ , Then the electrode is cleaned with deionized water to obtain the Pt/Au/PdCo/C catalyst.

Example 4:

Weigh 28.2mg PdCl ₂ and 9.6mg Co(NO ₃ ) ₂ (Pd/Co atomic ratio is 3:1) and dissolve in 100mL deionized water, add 80mg Vulcan XC-72 carbon powder and ultrasonically disperse for 30min. After uniform dispersion, 25mL of 25mmol L ^-1 sodium citrate aqueous solution was added dropwise, and then 25mL of 80mmol L ^-1 NaBH ₄ solution was slowly added dropwise under rapid stirring. After 30 minutes, the obtained product was filtered, washed with a large amount of deionized water, and dried in a vacuum oven at 80° C. for 8 hours to obtain a PdCo/C catalyst. The alloyed PdCo/C catalyst can be obtained by heat-treating the PdCo/C catalyst at 400° C. for 2 hours under a 5vol% H ₂ /Ar atmosphere.

Disperse 5 mg of alloyed PdCo/C catalyst in 2 mL of ethanol, and add 30 μL of 5% Nafion emulsion as a binder. After ultrasonic dispersion for 15 min, 20 μL of the slurry was pipetted and coated on the surface of a glassy carbon electrode as a working electrode. Place the working electrode in a solution of 50mmol L ^-1 H ₂ SO ₄ and 50mmol L ^-1 CuSO ₄ for Cu underpotential deposition: first, maintain a deposition potential of 420mV for 120s to cause underpotential deposition of Cu on the surface of PdCo nanoparticles, and then quickly Immerse the electrode in a mixed solution of 50mmol L ^-1 H ₂ SO ₄ and 1mmol L ^-1 HAuCl ₄ , let it stand for 4min to make the replacement reaction between Au ³⁺ and Cu ²⁺ , and then clean the surface of the electrode with deionized water. Repeat the underpotential deposition of Cu, then quickly place the electrode in the solution of 50mmol L ^-1 H ₂ SO ₄ and 1mmol L ^-1 K ₂ PtCl ₄ , let it stand for 4min to allow the substitution reaction between Pt ²⁺ and Cu ²⁺ , then Clean the electrode with deionized water to obtain the Pt/Au/PdCo/C catalyst.

Example 5:

Weigh 28.2mg PdCl ₂ and 9.6mg Co(NO ₃ ) ₂ (Pd/Co atomic ratio is 3:1) and dissolve in 100mL deionized water, add 80mg Vulcan XC-72 carbon powder and ultrasonically disperse for 30min. After uniform dispersion, 25mL of 25mmol L ^-1 sodium citrate aqueous solution was added dropwise, and then 25mL of 80mmol L ^-1 NaBH ₄ solution was slowly added dropwise under rapid stirring. After 30 minutes, the obtained product was filtered, washed with a large amount of deionized water, and dried in a vacuum oven at 80° C. for 8 hours to obtain a PdCo/C catalyst. The alloyed PdCo/C catalyst can be obtained by heat-treating the PdCo/C catalyst at 400° C. for 2 hours under a 5vol% H ₂ /Ar atmosphere.

Disperse 5 mg of alloyed PdCo/C catalyst in 2 mL of ethanol, and add 30 μL of 5% Nafion emulsion as a binder. After ultrasonic dispersion for 15 min, 20 μL of the slurry was pipetted and coated on the surface of a glassy carbon electrode as a working electrode. The working electrode was placed in a mixed solution of 50mmol L ^-1 H ₂ SO ₄ and 50mmol L ^-1 CuSO ₄ for Cu underpotential deposition: first, the deposition potential of 520mV was maintained for 120s to make Cu underpotential deposition on the surface of PdCo nanoparticles, and then Quickly immerse the electrode in the mixed solution of 50mmolL ^-1 H ₂ SO ₄ and 1mmol L ^-1 HAuCl ₄ , let it stand for 4min to make the replacement reaction between Au ³⁺ and Cu ²⁺ , and then clean the surface of the electrode with deionized water. The underpotential deposition of Cu was repeated, and then the electrode was quickly placed in the mixed solution of 50mmol L ^-1 H ₂ SO ₄ and 1mmol L ^-1 K ₂ PtCl ₄ , and stood for 4min to allow the substitution reaction between Pt ²⁺ and Cu ²⁺ , Then the electrode is cleaned with deionized water to obtain the Pt/Au/PdCo/C catalyst.

Embodiment 6:

Weigh 28.2mg PdCl ₂ and 9.6mg Co(NO ₃ ) ₂ (Pd/Co atomic ratio is 3:1) and dissolve in 100mL deionized water, add 80mg Vulcan XC-72 carbon powder and ultrasonically disperse for 30min. After uniform dispersion, 25mL of 25mmol L ^-1 sodium citrate aqueous solution was added dropwise, and then 25mL of 80mmol L ^-1 NaBH ₄ solution was slowly added dropwise under rapid stirring. After 30 minutes, the obtained product was filtered, washed with a large amount of deionized water, and dried in a vacuum oven at 80° C. for 8 hours to obtain a PdCo/C catalyst. The alloyed PdCo/C catalyst can be obtained by heat-treating the PdCo/C catalyst at 400° C. for 2 hours under a 5vol% H ₂ /Ar atmosphere.

Disperse 5 mg of alloyed PdCo/C catalyst in 2 mL of ethanol, and add 30 μL of 5% Nafion emulsion as a binder. After ultrasonic dispersion for 15 min, 20 μL of the slurry was pipetted and coated on the surface of a glassy carbon electrode as a working electrode. The working electrode was placed in a mixed solution of 50mmol L ^-1 H ₂ SO ₄ and 50mmol L ^-1 CuSO ₄ for Cu underpotential deposition: firstly, the deposition potential of 390mV was maintained for 1s to cause underpotential deposition of Cu on the surface of PdCo nanoparticles, and then Quickly immerse the electrode in a solution of 50mmol L ^-1 H ₂ SO ₄ and 1mmol L ^-1 HAuCl ₄ , let it stand for 4 minutes to allow the substitution reaction between Au ³⁺ and Cu ²⁺ , and then clean the surface of the electrode with deionized water. The underpotential deposition of Cu was repeated, and then the electrode was quickly placed in the mixed solution of 50mmol L ^-1 H ₂ SO ₄ and 1mmol L ^-1 K ₂ PtCl ₄ , and stood for 4min to allow the substitution reaction between Pt ²⁺ and Cu ²⁺ , Then the electrode is cleaned with deionized water to obtain the Pt/Au/PdCo/C catalyst.

Embodiment 7:

Weigh 28.2mg PdCl ₂ and 9.6mg Co(NO ₃ ) ₂ (Pd/Co atomic ratio is 3:1) and dissolve in 100mL deionized water, add 80mg Vulcan XC-72 carbon powder and ultrasonically disperse for 30min. After uniform dispersion, 25mL of 25mmol L ^-1 sodium citrate aqueous solution was added dropwise, and then 25mL of 80mmol L ^-1 NaBH ₄ solution was slowly added dropwise under rapid stirring. After 30 minutes, the obtained product was filtered, washed with a large amount of deionized water, and dried in a vacuum oven at 80° C. for 8 hours to obtain a PdCo/C catalyst. The alloyed PdCo/C catalyst can be obtained by heat-treating the PdCo/C catalyst at 400° C. for 2 hours under a 5vol% H ₂ /Ar atmosphere.

Disperse 5 mg of alloyed PdCo/C catalyst in 2 mL of ethanol, and add 30 μL of 5% Nafion emulsion as a binder. After ultrasonic dispersion for 15 min, 20 μL of the slurry was pipetted and coated on the surface of a glassy carbon electrode as a working electrode. The working electrode was placed in a mixed solution of 50mmol L ^-1 H ₂ SO ₄ and 50mmol L ^-1 CuSO ₄ for Cu underpotential deposition: first, the deposition potential of 390mV was maintained for 40s to cause underpotential deposition of Cu on the surface of PdCo nanoparticles, and then Quickly immerse the electrode in a solution of 50mmol L ^-1 H ₂ SO ₄ and 1mmol L ^-1 HAuCl ₄ , let it stand for 4 minutes to allow the substitution reaction between Au ³⁺ and Cu ²⁺ , and then clean the surface of the electrode with deionized water. The underpotential deposition of Cu was repeated, and then the electrode was quickly placed in the mixed solution of 50mmol L ^-1 H ₂ SO ₄ and 1mmol L ^-1 K ₂ PtCl ₄ , and stood for 4min to allow the substitution reaction between Pt ²⁺ and Cu ²⁺ , Then the electrode is cleaned with deionized water to obtain the Pt/Au/PdCo/C catalyst.

Embodiment 8:

Weigh 28.2mg PdCl ₂ and 9.6mg Co(NO ₃ ) ₂ (Pd/Co atomic ratio is 3:1) and dissolve in 100mL deionized water, add 80mg Vulcan XC-72 carbon powder and ultrasonically disperse for 30min. After uniform dispersion, 25mL of 25mmol L ^-1 sodium citrate aqueous solution was added dropwise, and then 25mL of 80mmol L ^-1 NaBH ₄ solution was slowly added dropwise under rapid stirring. After 30 minutes, the obtained product was filtered, washed with a large amount of deionized water, and dried in a vacuum oven at 80° C. for 8 hours to obtain a PdCo/C catalyst. The alloyed PdCo/C catalyst can be obtained by heat-treating the PdCo/C catalyst at 400° C. for 2 hours under a 5vol% H ₂ /Ar atmosphere.

Disperse 5 mg of alloyed PdCo/C catalyst in 2 mL of ethanol, and add 30 μL of 5% Nafion emulsion as a binder. After ultrasonic dispersion for 15 min, 20 μL of the slurry was pipetted and coated on the surface of a glassy carbon electrode as a working electrode. The working electrode was placed in a mixed solution of 50mmol L ^-1 H ₂ SO ₄ and 50mmol L ^-1 CuSO ₄ for Cu-UPD: firstly, the deposition potential of 390mV was maintained for 300s for CU-UPD, and then the electrode was quickly immersed in 50mmol L ^-1 In the mixed solution of H ₂ SO ₄ and 1 mmol L ^-1 HAuCl ₄ , let stand for 4 minutes to make the replacement reaction complete, and then clean the electrode with deionized water. Repeat the Cu-UPD process, then quickly place the electrode in a mixed solution of 50mmol L ^-1 H ₂ SO ₄ and 1mmolL ^-1 K ₂ PtCl ₄ , let it stand for 4min to complete the replacement reaction, and then clean the electrode with deionized water The Pt/Au/PdCo/C catalyst can be obtained.

Comparative Example 1: Alloyed PdCo/C Catalyst

Weigh 28.2mg PdCl ₂ and 9.6mg Co(NO ₃ ) ₂ (Pd/Co atomic ratio is 3:1) and dissolve in 100mL deionized water, add 80mg Vulcan XC-72 carbon powder and ultrasonically disperse for 30min. After uniform dispersion, 25mL of 25mmol L ^-1 sodium citrate aqueous solution was added dropwise, and then 25mL of 80mmol L ^-1 NaBH ₄ solution was slowly added dropwise under rapid stirring. After 30 minutes, the obtained product was filtered, washed with a large amount of deionized water, and dried in a vacuum oven at 80° C. for 8 hours to obtain a PdCo/C catalyst.

The alloyed PdCo/C catalyst can be obtained by heat-treating the PdCo/C catalyst (400° C., 5vol% H ₂ /Ar, 2 h).

Comparative example 2: Pt/PdCo/C catalyst

Disperse 5 mg of alloyed PdCo/C catalyst in 2 mL of ethanol, and add 30 μL of 5% Nafion emulsion as a binder. After ultrasonic dispersion for 15 min, 20 μL of the slurry was pipetted and coated on the surface of a glassy carbon electrode as a working electrode. Place the working electrode in 50mmol L ^-1 H ₂ SO ₄ and 50mmol L ^-1 CuSO ₄ solution for Cu-UPD: Firstly, Cu-UPD was performed at a deposition potential of 390mV for 120s, and then the electrode was quickly placed in 50mmol L ^-1 In the mixed solution of H ₂ SO ₄ and 1 mmol L ^-1 K ₂ PtCl ₄ , let stand for 4 minutes to make the replacement reaction complete, and then clean the electrode with deionized water to obtain the Pt/PdCo/C catalyst.

Comparative example 3: Pt/C catalyst

Commercial 20wt.% Pt/C catalyst (E-TEK company).

Figure 1 is the Cu dissolution curve obtained by depositing at different deposition potentials for 120s, and then scanning from this potential to 820mV at a scan rate of 20mV s ^-1 . The selected potentials are all higher than the bulk deposition potential of Cu, which is 340mV. It can be seen from Figure 1 that as the deposition potential shifts negatively, the oxidation peaks at 470mV and 580mV gradually increase, and when the deposition potential shifts negatively to 380mV, the oxidation peak of Cu in the bulk phase begins to appear, indicating that Cu has already occurred at this potential Bulk phase deposition, so the deposition potential is selected as 390mV.

Figure 2 is the Cu dissolution curve obtained by scanning from 390mV to 820mV at a scan rate of 20mV s ^-1 after different deposition times with 390mV as the deposition potential. It can be seen from Figure 2 that with the prolongation of the deposition time, the anodic dissolution peak of Cu gradually increases, and the dissolution curves basically coincide after 120 s, indicating that the underpotential deposition of Cu has been saturated, and with the further prolongation of the deposition time, there is no longer Cu in the Underpotential deposition occurs on the PdCo surface. This self-termination phenomenon in the UPD process stems from the strong interaction between Cu and the noble metal Pd. When the surface of Pd particles is completely covered by Cu monolayer, Cu cannot be terminated by underpotential deposition on the surface of Cu atoms.

Fig. 3 is the CV curve and ORR polarization curve of the sample prepared according to Example 1 and Comparative Example 2 in 0.1M HClO ₄ solution. It can be seen from Figure 3(a) that compared with the Pt/PdCo/C catalyst, the hydrogen adsorption and desorption peaks of Pt/Au/PdCo/C are reduced, and the electrochemically active surface area calculated by integrating the hydrogen desorption peaks (ECSAs) are 149.3 and 144.3m ² g ^-1 , respectively, such high ECSAs may be caused by the highly dispersed Pt on the catalyst surface. At the same time, in the Pt/Au/PdCo/C catalyst, the redox peak of Pt at high potential decreases and moves to high potential, indicating that OH is more likely to be adsorbed and desorbed on the surface of Pt, which indicates that the catalytic activity of ORR will be improved. . It can be seen from Figure 3(b) that the introduction of Au between Pt and PdCo improves the ORR catalytic activity of the catalyst, and the half-wave potential of the ORR polarization curve is positively shifted from 0.878V to 0.90V, which is increased by 22mV.

Figure 4 is a comparison of kinetic current per unit mass of Pt in Example 1 and Comparative Examples 2 and 3 at a certain potential (0.85V and 0.9V). Compared with the Pt/C and Pt/PdCo/C catalysts, the Pt/Au/PdCo/C catalyst has 13 and 4 times higher ORR catalytic activity at 0.85 V, respectively, greatly improving the utilization of the noble metal Pt. The enhanced catalytic activity for ORR may be due to the contraction of the Pt lattice caused by the addition of Au, which modulates the d-band center of Pt and makes it easier for OH to desorb on Pt.

Fig. 5 shows the CV curves and ORR polarization curves of the samples prepared according to Example 1 and Comparative Example 2 before and after the stability test (100mVs ^-1 , 0.6-1.0V vs. NHE) in 0.1M HClO ₄ solution. It can be seen from Figure 5 that after 10k cycles of CV scanning, the half-wave potential of the ECSAs and ORR polarization curves of the Pt/PdCo/C catalyst decreased by 48.2% and 32mV, respectively; and after the stability test under the same conditions, the Pt/Au/PdCo The ECSAs of the /C catalyst decreased from 144.3 to 104m ² g ^-1 , decreased by 27.9%, but the ORR catalytic activity did not decline significantly, and the half-wave potential only shifted negatively by 13mV. The above results show that the stability of Pt/Au/PdCo/C has been significantly improved on the basis of Pt/PdCo/C.

FIG. 6 is a TEM photo of the samples prepared according to Example 1 and Comparative Example 2 before and after the stability test in 0.1M HClO ₄ solution. It can be seen from Figure 6 that before the stability test, the nanoparticles in the Pt/PdCo/C and Pt/Au/PdCo/C catalysts were more uniformly distributed on the carbon support, with average particle sizes of 5.3 and 5.5 nm, respectively. . After 10k cycles of CV scanning, the nanoparticles in Pt/PdCo/C were severely aggregated, and the surface became uneven, and the catalyst morphology was severely damaged, resulting in a large attenuation of the catalytic activity of ECSAs and ORR in the CV curves. In contrast, the morphology of Pt/Au/PdCo/C undergoing the same electrochemical stability test did not change greatly, but the particle size of the nanoparticles increased slightly (5.5 to 6.6nm). The above results indicated that the stability of the catalyst was significantly improved after the introduction of Au submonolayer between Pt and PdCo.

Claims (10)

1. a Pt/Au/PdCo/C catalyst, is characterized in that:

Catalyst is the metal core shell structure that carbon carries, and the metal in catalyst is with PdCo alloy for core, and to be positioned at the Pt on surface for shell, Au is between Pt shell and PdCo core, and in catalyst, Pt is single layer structure, and Au is time single layer structure; In catalyst, metal quality accounts for the 12-46% of gross mass; Wherein the mol ratio of Pd and Co is 5:1-1:1; The mol ratio of Pd and Au is 5:1-12:1; The mol ratio of Pd and Pt is 10:1-20:1; Catalyst adopts the method for Cu-UPD-displacement to be incorporated between surperficial Pt layer and PdCo core as secondary individual layer by Au and prepares.

2. a preparation method for catalyst described in claim 1, is characterized in that: comprise the following steps,

(1) preparation of alloying PdCo/C

A. in deionized water, PdCl is added ₂and/or Pd (NO ₃) ₂, add Co (NO simultaneously ₃) ₂, CoCl ₂, CoBr ₂, CoSO ₄, Co (COOH) ₂in one or more formed mixtures, stir make it to mix, in mixed liquor, add carbon carrier afterwards, and ultrasonic disperse is even to mixed liquor;

B. in above-mentioned steps (1) a gained mixed liquor, drip sodium citrate aqueous solution, and dropwise drip NaBH under the condition stirred ₄the aqueous solution, filters to obtain solid matter after leaving standstill, and adopts deionized water to wash gained solid matter afterwards, and it is dry that gained material after washing is placed in vacuum drying oven, obtains PdCo/C;

C. step (1) b gained PdCo/C is heat-treated in hydrogen and inert gas gaseous mixture, obtain alloying PdCo/C;

(2) preparation of Pt/Au/PdCo/C catalyst

A. in ethanol, add above-mentioned steps (1) c gained alloying PdCo/C, stir after making it to mix and add Nafion emulsion, and ultrasonic disperse is even to mixed liquor;

B. pipette above-mentioned steps (2) a gained mixed liquor, and be coated on glassy carbon electrode surface as work electrode, Pt silk is to electrode, and saturated calomel electrode is reference electrode;

C. above-mentioned steps (2) b gained work electrode is placed in H ₂sO ₄and CuSO ₄under the sedimentation potential of 350-520mV, maintain 1-300s in mixed solution, then electrode is immersed H ₂sO ₄and HAuCl ₄also leave standstill 1-10min in mixed solution and carry out displacement reaction, then with deionized water, electrode clean is clean;

D. above-mentioned steps (2) c gained work electrode is placed in H ₂sO ₄and CuSO ₄under the sedimentation potential of 350-520mV, maintain 1-300s in mixed solution, then electrode is immersed H ₂sO ₄and K ₂ptCl ₄also leave standstill 1-10min in mixed solution and carry out displacement reaction, then with deionized water, electrode clean is clean, namely obtain Pt/Au/PdCo/C catalyst.

3. the preparation method of catalyst as claimed in claim 2, is characterized in that:

Pd in mixture described in step (1) a ²⁺and Co ²⁺mol ratio be 5:1 ~ 1:1; Pd in described mixture ²⁺concentration be 10-100mmol L ^-1.

4. the preparation method of catalyst as claimed in claim 2, is characterized in that:

Metal quality in alloying PdCo/C described in step (1) accounts for the 10-40% of gross mass.

5. the preparation method of catalyst as claimed in claim 2, is characterized in that:

Described in step (1) b, the concentration of sodium citrate aqueous solution is 10-50mmol L ^-1, consumption is 10-50mL; Described NaBH ₄the concentration of the aqueous solution is 10-100mmol L ^-1, consumption is 10-50mL; The described vacuumize time is 5-20 hour.

6. the preparation method of catalyst as claimed in claim 2, is characterized in that:

Inert atmosphere described in step (1) c is the mixture of one or two or more kinds in argon gas, helium, nitrogen; Described hydrogen volume accounts for the 1-10% of volume of gas; Described heat treatment temperature is 200-600 DEG C; Described heat treatment time is 1-3h.

7. the preparation method of catalyst as claimed in claim 2, is characterized in that:

Described in step (2) a, the concentration of PdCo/C in ethanol is 0.5-5mg mL ^-1; The mass ratio of described Nafion and PdCo/C is 1:10-1:1.

8. the preparation method of catalyst as claimed in claim 2, is characterized in that:

H described in step (2) c and step (2) d ₂sO ₄and CuSO ₄in mixed solution, the thing mass ratio of the two is 5:1-1:2; Described H ₂sO ₄and HAuCl ₄in mixed solution, the thing mass ratio of the two is 100:1-20:1; Described H ₂sO ₄and K ₂ptCl ₄in mixed solution, the thing mass ratio of the two is 100:1-20:1; H in above-mentioned three kinds of mixed solutions ₂sO ₄concentration be 20-100mmol L ^-1.

9. the preparation method of catalyst as claimed in claim 2, is characterized in that:

Described carbon carrier is: one or more the mixture in XC-72R, BP2000, acetylene black, carbon nano-tube, graphite.

10. an application for Pt/Au/PdCo/C catalyst described in claim 1, is characterized in that: described Pt/Au/PdCo/C catalyst can be used as metal air fuel cell oxygen reduction catalyst, Proton Exchange Membrane Fuel Cells oxygen reduction catalyst or direct liquid fuel battery oxygen reduction catalyst.