CN102476053B - Preparation method of Pd-Ag/C catalyst - Google Patents

Abstract

A method for preparing a Pd-Ag/C catalyst, wherein the mass fraction of Pd is 1-30%, and the mass of Ag is not more than 25% of the Pd content. The catalyst is obtained by an impregnation reduction method, and its preparation includes three steps: (1) dispersion of carbon support, (2) preparation of impregnation solution and (3) preparation of Pd-Ag/C catalyst. The preparation process of the catalyst does not require the addition of a protective agent to regulate the particle size and alloy degree of the catalyst. It has high catalytic activity for the oxidation of small molecule alcohols in alkaline media and good stability. The preparation process is non-toxic and pollution-free. It can be scaled up and can be used as a base It is an electrochemical oxidation catalyst for small molecule alcohols in alkaline media, especially suitable for small molecule alcohol fuel oxidation catalysts for alkaline direct alcohol fuel cells.

Description

A kind of preparation method of Pd-Ag/C catalyst

technical field

The invention relates to a small molecule alcohol oxidation catalyst under alkaline conditions, in particular to a preparation method for a small molecule alcohol fuel oxidation catalyst used in an alkaline fuel cell.

Background technique

With the research and development of anion exchange membranes, the problem of carbonation in alkaline fuel cells has been solved to a certain extent. In alkaline solution, on the one hand, due to the fast kinetics of electrochemical oxidation and oxygen reduction of small molecule fuels such as methanol and ethanol, the catalytic efficiency of fuel cells can be greatly improved; on the other hand, because non-Pt electrocatalysts can be used , can reduce the cost of fuel cells. Therefore, alkaline fuel cells have attracted extensive attention of researchers.

The literature (Electrochemistry Communications 2007; 9: 2760-2763) pointed out that the catalytic activity of carbon-supported Pd electrocatalysts in catalyzing the oxidation of alcohols in alkaline media is higher than that of Pt electrocatalysts, and compared with Pt, Pd has low price and abundant reserves. , and has the same outer electronic structure as Pt, and can be used as a substitute metal for Pt-based catalysts. At present, the research on Pd-based catalysts mainly focuses on the change of carbon support, the change of catalyst micro-morphology, and the addition of other metals or metal oxides. However, there is still no relatively recognized catalyst with high catalytic activity, good stability and low cost.

According to the d-band principle, the doping of Ag (a=0.409nm) with a large lattice constant into Pd (a=0.389nm) with a small lattice constant will cause the d-band energy of Pd atoms to increase, and the reactant The binding ability of the catalyst is increased, thereby improving its catalytic activity, reducing the amount of Pd, and reducing the cost.

The literature (Applied Catalysis B: Environmental 2009; 91: 507-515) prepared Pd-Ag/C catalyst by co-reduction method. Similar to the conventional method, in order to reduce the particle size of the catalyst, a protective agent is added in the preparation process, so the catalytic activity and stability of the catalyst prepared by this method are still unsatisfactory, and further work is still needed on the basis of the existing technology. improvement of.

Contents of the invention

The present invention aims at the deficiencies of the prior art, and aims to provide a small molecule alcohol fuel oxidation electrocatalyst for alkaline fuel cells and a preparation method thereof, the catalyst has high catalytic activity and good stability for the electrooxidation of small molecule alcohol fuels , compared with the commonly used Pt-based catalysts, the source of raw materials is abundant and the cost is low, and the preparation process is simple, which is conducive to the large-scale production of products.

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

A preparation method of Pd-Ag/C catalyst comprises the following steps,

1) Dispersion of the carbon carrier: Mix the carbon carrier with absolute ethanol and stir to disperse the carbon carrier evenly in the ethanol to form a slurry; the carbon carrier is easier to disperse in ethanol due to its own hydrophilic and hydrophobic characteristics, forming a uniform For slurry, if water is used as dispersant, the carbon carrier is easy to re-coagulate after the stirring is stopped.

2) Preparation of dipping solution:

Mix and dissolve Pd(NO ₃ ) ₂ , or Pd(NO ₃ ) ₂ and AgNO ₃ in deionized water to form a solution, and add or pour the solution dropwise into the container containing the carbon carrier slurry in step (1) ; Pd(NO ₃ ) ₂ and AgNO ₃ are easily soluble in aqueous solution, which is conducive to uniform impregnation on the surface of carbon support;

Or dissolve Pd(NO ₃ ) ₂ and AgNO ₃ in deionized water to form solutions, and follow the order of Pd(NO ₃ ) ₂ solution first and then AgNO ₃ solution or first AgNO ₃ solution and then Pd(NO ₃ ) ₂ solution. Add dropwise or pour it into the container containing the carbon carrier slurry in step (1); the metal precursor Pd(NO ₃ ) ₂ , or the mixed solution of Pd(NO ₃ ) ₂ and AgNO ₃ is added in different order, and the carbon Different microstructures are formed on the surface of the carrier; usually, if the reaction is controlled by diffusion, the eggshell type is suitable; when the reaction is controlled by kinetics: uniform distribution is suitable; if there are toxic substances in the medium, the protein and egg yolk type are suitable. The metal atomic structure of the final catalyst can be adjusted by different dropping sequences of the precursors, and then the catalytic activity of the catalyst can be adjusted;

The volume of deionized water in the immersion system is 0.5-1.5 times the volume of ethanol; immersion time ≥ 3h;

3) Preparation of Pd-Ag/C catalyst:

a. Evaporate the impregnation solution obtained in the above-mentioned steps (2); prevent the metal precursor from agglomerating into large particles on the surface of the carbon carrier during the drying process, affecting the catalytic activity of the catalyst;

b. Dry the evaporated matter obtained in the above step (3)a at 50-85°C for ≥5h to obtain a black powder; if the temperature is too low, it cannot be fully dried, and if the temperature is too high, the catalyst particles are easy to aggregate and grow, which affects the catalytic activity;

c. Put the black powder obtained in the above steps in a tube furnace and process it under an inert gas atmosphere. Heat treatment for 20-60min, then program the temperature to 150-700℃ at a rate of 1-10℃/min;

d. Keep the final temperature in the above steps, feed the mixed gas of _H2 and inert gas with a volume fraction of 1-15% in the tube furnace, after heat treatment for 1-3h, wash and dry the black powder to obtain the target The product Pd-Ag/C catalyst, the active component in the catalyst is Pd, or Pd and Ag, the total mass content of the active component in the catalyst is 1-30%, and the mass of Ag is not more than 25% of the Pd content.

The ratio of the carbon carrier to absolute ethanol is that the volume of absolute ethanol added per 20 mg of carbon carrier is 5-40 mL.

The mass concentration of Pd(NO ₃ ) ₂ in the impregnation system prepared in the preparation process of the above step 2) is 0.02 mg/mL to 7.8 mg/mL, and the mass concentration of AgNO ₃ is 0.005 mg/mL to 1.95 mg/mL.

Put the black powder obtained in the above step (3)b into a quartz or ceramic vessel after being ground and weighed; then put it into a tube furnace.

In the above step (3)a, the impregnating liquid obtained in the above step (2) is rotary evaporated to dryness at 30-70°C.

The impregnation process is carried out under the condition of magnetic stirring at 0-50° C., and the impregnation is ≥3 hours.

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

The inert atmosphere is one or a mixture of nitrogen, argon, and helium.

The Pd-Ag/C catalyst can be used as an electrocatalyst for the oxidation of small molecule alcohol fuels in alkaline media; the small molecule alcohol fuels are C1-C6 alcohols, such as methanol, ethanol, propanol, ethylene glycol, glycerol Alcohol, n-butanol, glucose, etc.

Compared with the prior art, the preparation method of the Pd-Ag/C catalyst of the present invention has the following advantages:

1. The Pd-Ag/C catalyst prepared by the method of the present invention can be controlled by controlling _H flow rate, reduction time and reduction temperature to regulate and control the particle size, crystal structure, alloy degree and other catalyst microscopic appearances of the catalyst, which can Achieve nanoscale design of catalysts.

2. Adopt the method described in the present invention to prepare Pd-Ag/C catalyst, do not introduce protective agent to control the growth of particle size in the preparation process, the phenomenon that protective agent is difficult to remove and suppress catalytic activity can not occur, so the activity of conventional catalyst high.

3. The Pd-Ag/C catalyst prepared by the method of the present invention can regulate the metal atomic structure of the final catalyst through different dropping sequences of the precursors, thereby improving the catalytic activity of the catalyst;

4. Adopt the method described in the present invention to prepare Pd-Ag/C catalyst, no toxic substances participate in the preparation process, safe and pollution-free, and conducive to environmental protection;

5. Adopting the method of the present invention to prepare the Pd-Ag/C catalyst, the preparation process is simple and easy, which is conducive to the scale-up production of the catalyst and accelerates its industrialization process;

6. Adopt the Pd-Ag/C catalyst prepared by the method of the present invention, can control the size of the catalyst particle while ensuring that the catalyst is fully dry by selecting a suitable drying temperature, and then improve the catalytic activity;

7. adopt the method for preparing Pd-Ag/C catalyst of the present invention, the selection _of ethanol dispersant helps carbon support to disperse _evenly therein _; The surface of the carbon carrier is evenly impregnated;

8. The Pd-Ag/C catalyst prepared by the method of the present invention has high electro-oxidation catalytic activity to small molecule alcohol fuels in alkaline medium, good stability, and is obviously better than commercial products for ethanol oxidation. Pt/C catalyst;

Description of drawings:

FIG. 1 is the XRD spectrum of the samples prepared according to Comparative Examples 1, 3, 4, and 5.

Figure 2 is the XRD spectrum of samples prepared according to Comparative Examples 5 and 6 and Examples 1, 2, 3, 4 and 9.

Fig. 3 is an XRD spectrum of samples prepared according to Examples 5-9.

Fig. 4 is the CV graph of the samples prepared according to Comparative Examples 1-5 in _N2 saturated 1.0M NaOH electrolyte.

Fig. 5 is a CV diagram of samples prepared according to Comparative Examples 1-5 in N ₂ saturated 1.0M NaOH+1.0MCH ₃ CH ₂ OH electrolyte.

Fig. 6 is the CV diagram of samples prepared according to Comparative Examples 5, 7 and Examples 1, 2, 3, 4, 9 in N ₂ saturated 1.0M NaOH electrolyte.

Fig. 7 is a CV diagram of samples prepared according to Comparative Examples 5 and 7 and Examples 1, 2, 3, 4 and 9 in N ₂ saturated 1.0M NaOH+1.0M CH ₃ CH ₂ OH electrolyte.

Fig. 8 is a CV diagram of samples prepared according to Examples 5-9 in N ₂ saturated 1.0M NaOH+1.0MCH ₃ CH ₂ OH electrolyte.

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: 20% Pd ₄ Ag ₁ /C-500 (20% means that the mass content of active components Pd and Ag is 20%, wherein the mol ratio of Pd and Ag is 4: 1, and -500 means that the reduction temperature is 500℃)

First, ultrasonically disperse 80mg of Vulcan XC-72 carbon black in 30mL of absolute ethanol, and then add 30mL of a mixed aqueous solution of 2.04mL of Pd(NO ₃ ) ₂ aqueous solution with a mass fraction of 7.8mg/mL and 6.4mg of AgNO ₃ . The above solution was impregnated and stirred at room temperature for 6 hours, then the solvent was removed by a rotary evaporator at 65°C, and dried at 65°C to obtain a black powder. The above black powder was ground, weighed, and placed in a quartz boat, then transferred to a tube furnace, programmed to heat up to 120°C at a rate of 5°C min ^-1 under _N2 atmosphere, and treated at this temperature for 0.5h , and then the temperature was programmed to 500°C at a rate of 5°C min ^-1 , and a mixed gas of H ₂ and N ₂ with a volume fraction of 5% was passed, and the constant temperature heat treatment was carried out for 2 hours to obtain the target product of 20% Pd ₄ Ag ₁ /C- 500 electrocatalyst.

Embodiment 2: 20%Pd ₃ Ag ₁ /C-500 (14.95%Pd-5.05%Ag/C-500) (20% means that the mass content of active component Pd and Ag is 20%, wherein Pd and Ag The molar ratio is 3:1, -500 means the reduction temperature is 500°C)

First, ultrasonically disperse 80mg of Vulcan XC-72 carbon black in 30mL of absolute ethanol, and then add 30mL of a mixed aqueous solution of 1.92mL of Pd(NO ₃ ) ₂ aqueous solution with a mass fraction of 7.8mg/mL and 8.0mg of AgNO ₃ . The above solution was impregnated and stirred at room temperature for 6 hours, then the solvent was removed by a rotary evaporator at 65°C, and dried at 65°C to obtain a black powder. The above black powder was ground, weighed, and placed in a quartz boat, then transferred to a tube furnace, programmed to heat up to 120°C at a rate of 5°C min ^-1 under _N2 atmosphere, and treated at this temperature for 0.5h , and then the temperature was programmed to 500°C at a rate of 5°C min ^-1 , and a mixed gas of H ₂ and N ₂ with a volume fraction of 5% was passed, and the constant temperature heat treatment was performed for 2 hours, and the target product was 20% Pd ₃ Ag ₁ /C- 500 electrocatalyst.

Embodiment 3: 20%Pd ₁ Ag ₁ /C-500 (20% refers to that the mass content of active component Pd and Ag is 20%, wherein the mol ratio of Pd and Ag is 1: 1,-500 represents that reduction temperature is 500℃)

First, ultrasonically disperse 80mg of Vulcan XC-72 carbon black in 30mL of absolute ethanol, and then add 30mL of a mixed aqueous solution of 1.27mL of Pd(NO ₃ ) ₂ aqueous solution with a mass fraction of 8.7mg/mL and 15.9mg of AgNO ₃ . The above solution was impregnated and stirred at room temperature for 6 h, and then the solvent was removed using a rotary evaporator at 65° C., and dried at 65° C. to obtain a black powder. The above black powder was ground, weighed, and placed in a quartz boat, then transferred to a tube furnace, programmed to heat up to 120°C at a rate of 5°C min ^-1 under _N2 atmosphere, and treated at this temperature for 0.5h , and then the temperature was programmed to 500°C at a rate of 5°C min ^-1 , and a mixture of H ₂ and N ₂ with a volume fraction of 5% was passed through, and the constant temperature heat treatment was performed for 2 hours to obtain the target product of 20% Pd ₁ Ag ₁ /C- 500 electrocatalyst.

Example 4: 20%Pd ₁ Ag ₂ /C-500 (20% means that the mass content of active components Pd and Ag is 20%, wherein the molar ratio of Pd and Ag is 1: 2, and -500 means that the reduction temperature is 500℃)

First, ultrasonically disperse 80mg of Vulcan XC-72 carbon black in 30mL of absolute ethanol, and then add 30mL of a mixed aqueous solution of 0.85mL of Pd(NO ₃ ) ₂ aqueous solution with a mass fraction of 7.8mg/mL and 21.1mg of AgNO ₃ . The above solution was impregnated and stirred at room temperature for 6 h, and then the solvent was removed using a rotary evaporator at 65° C., and dried at 65° C. to obtain a black powder. The above black powder was ground, weighed, and placed in a quartz boat, then transferred to a tube furnace, programmed to heat up to 120°C at a rate of 5°C min ^-1 under _N2 atmosphere, and treated at this temperature for 0.5h , and then the temperature was programmed to 500°C at a rate of 5°C min ^-1 , and a mixed gas of H ₂ and N ₂ with a volume fraction of 5% was passed, and the constant temperature heat treatment was performed for 2 hours, and the target product was obtained as 20% Pd ₁ Ag ₂ /C- 500 electrocatalyst.

Embodiment 5: 20%Pd ₂ Ag ₁ /C-150 (20% means that the mass content of active component Pd and Ag is 20%, wherein the molar ratio of Pd and Ag is 2: 1, and -150 means that the reduction temperature is 150℃)

First, 80mg of Vulcan XC-72 carbon black was ultrasonically dispersed in 30mL of absolute ethanol, and then 30mL of a mixed aqueous solution of 1.70mL of Pd(NO ₃ ) ₂ aqueous solution with a mass fraction of 7.8mg/mL and 10.7mg of AgNO ₃ was added. The above solution was impregnated and stirred at room temperature for 6 h, and then the solvent was removed using a rotary evaporator at 65° C., and dried at 65° C. to obtain a black powder. The above black powder was ground, weighed, and placed in a quartz boat, then transferred to a tube furnace, programmed to heat up to 120°C at a rate of 5°C min ^-1 under _N2 atmosphere, and treated at this temperature for 0.5h , and then the temperature was programmed to 150°C at a rate of 5°C min ^-1 , and a mixture of H ₂ and N ₂ with a volume fraction of 5% was passed through, and the constant temperature heat treatment was carried out for 2 hours to obtain the target product of 20% Pd ₂ Ag ₁ /C- 150 electrocatalysts.

Embodiment 6: 20%Pd ₂ Ag ₁ /C-200 (20% means that the mass content of active components Pd and Ag is 20%, wherein the molar ratio of Pd and Ag is 2: 1, and -200 means that the reduction temperature is 200℃)

First, 80mg of Vulcan XC-72 carbon black was ultrasonically dispersed in 30mL of absolute ethanol, and then 30mL of a mixed aqueous solution of 1.70mL of Pd(NO ₃ ) ₂ aqueous solution with a mass fraction of 7.8mg/mL and 10.7mg of AgNO ₃ was added. The above solution was impregnated and stirred at room temperature for 6 h, and then the solvent was removed using a rotary evaporator at 65° C., and dried at 65° C. to obtain a black powder. The above black powder was ground, weighed, and placed in a quartz boat, then transferred to a tube furnace, programmed to heat up to 120°C at a rate of 5°C min ^-1 under _N2 atmosphere, and treated at this temperature for 0.5h , and then the temperature was programmed to 150°C at a rate of 5°C min ^-1 , and a mixture of H ₂ and N ₂ with a volume fraction of 5% was passed through, and the constant temperature heat treatment was carried out for 2 hours to obtain the target product of 20% Pd ₂ Ag ₁ /C- 200 electrocatalysts.

Embodiment 7: 20%Pd ₂ Ag ₁ /C-300 (20% means that the mass content of active component Pd and Ag is 20%, wherein the molar ratio of Pd and Ag is 2: 1, and -300 means that the reduction temperature is 300℃)

First, 80mg of Vulcan XC-72 carbon black was ultrasonically dispersed in 30mL of absolute ethanol, and then 30mL of a mixed aqueous solution of 1.70mL of Pd(NO ₃ ) ₂ aqueous solution with a mass fraction of 7.8mg/mL and 10.7mg of AgNO ₃ was added. The above solution was impregnated and stirred at room temperature for 6 h, and then the solvent was removed using a rotary evaporator at 65° C., and dried at 65° C. to obtain a black powder. The above black powder was ground, weighed, and placed in a quartz boat, then transferred to a tube furnace, programmed to heat up to 120°C at a rate of 5°C min ^-1 under _N2 atmosphere, and treated at this temperature for 0.5h , and then the temperature was programmed to 150°C at a rate of 5°C min ^-1 , and a mixture of H ₂ and N ₂ with a volume fraction of 5% was passed through, and the constant temperature heat treatment was carried out for 2 hours to obtain the target product of 20% Pd ₂ Ag ₁ /C- 300 electrocatalyst.

Embodiment 8: 20%Pd ₂ Ag ₁ /C-400 (20% means that the mass content of active components Pd and Ag is 20%, wherein the molar ratio of Pd and Ag is 2: 1, and -400 means that the reduction temperature is 400℃)

First, 80mg of Vulcan XC-72 carbon black was ultrasonically dispersed in 30mL of absolute ethanol, and then 30mL of a mixed aqueous solution of 1.70mL of Pd(NO ₃ ) ₂ aqueous solution with a mass fraction of 7.8mg/mL and 10.7mg of AgNO ₃ was added. The above solution was impregnated and stirred at room temperature for 6 h, and then the solvent was removed using a rotary evaporator at 65° C., and dried at 65° C. to obtain a black powder. The above black powder was ground, weighed, and placed in a quartz boat, then transferred to a tube furnace, programmed to heat up to 120°C at a rate of 5°C min ^-1 under _N2 atmosphere, and treated at this temperature for 0.5h , and then the temperature was programmed to 150°C at a rate of 5°C min ^-1 , and a mixture of H ₂ and N ₂ with a volume fraction of 5% was passed through, and the constant temperature heat treatment was carried out for 2 hours to obtain the target product of 20% Pd ₂ Ag ₁ /C- 400 electrocatalysts.

Embodiment 9: 20%Pd ₂ Ag ₁ /C-500 (20% means that the mass content of active components Pd and Ag is 20%, wherein the molar ratio of Pd and Ag is 2: 1, and -500 means that the reduction temperature is 500℃)

First, 80mg of Vulcan XC-72 carbon black was ultrasonically dispersed in 30mL of absolute ethanol, and then 30mL of a mixed aqueous solution of 1.70mL of Pd(NO ₃ ) ₂ aqueous solution with a mass fraction of 7.8mg/mL and 10.7mg of AgNO ₃ was added. The above solution was impregnated and stirred at room temperature for 6 h, and then the solvent was removed using a rotary evaporator at 65° C., and dried at 65° C. to obtain a black powder. The above black powder was ground, weighed, and placed in a quartz boat, then transferred to a tube furnace, programmed to heat up to 120°C at a rate of 5°C min ^-1 under _N2 atmosphere, and treated at this temperature for 0.5h , and then the temperature was programmed to 150°C at a rate of 5°C min ^-1 , and a mixture of H ₂ and N ₂ with a volume fraction of 5% was passed through, and the constant temperature heat treatment was carried out for 2 hours to obtain the target product of 20% Pd ₂ Ag ₁ /C- 500 electrocatalyst.

Comparative example 1: 20% Pd/C-150 (20% means that the mass content of the active component Pd is 20%, -150 means that the reduction temperature is 150°C)

First, 80 mg of Vulcan XC-72 carbon black was ultrasonically dispersed in 30 mL of absolute ethanol, and then 30 mL of an aqueous solution containing 2.56 mL of Pd(NO ₃ ) ₂ with a mass fraction of 7.8 mg/mL was added. The above solution was impregnated and stirred at room temperature for 6 h, and then the solvent was removed using a rotary evaporator at 65° C., and dried at 65° C. to obtain a black powder. The above black powder was ground, weighed, and placed in a quartz boat, then transferred to a tube furnace, programmed to heat up to 120°C at a rate of 5°C min ^-1 under _N2 atmosphere, and treated at this temperature for 0.5h , and then the temperature was programmed to 150°C at a rate of 5°C min ^-1 , a mixture of H ₂ and N ₂ with a volume fraction of 5% was passed, and the constant temperature heat treatment was performed for 2 hours to obtain the target product 20% Pd/C-150 electrocatalyst.

Comparative example 2: 20%Pd/C-200 (20% means that the mass content of the active component Pd is 20%, -200 means that the reduction temperature is 200°C)

First, 80 mg of Vulcan XC-72 carbon black was ultrasonically dispersed in 30 mL of absolute ethanol, and then 30 mL of an aqueous solution containing 2.56 mL of Pd(NO ₃ ) ₂ with a mass fraction of 7.8 mg/mL was added. The above solution was impregnated and stirred at room temperature for 6 h, and then the solvent was removed using a rotary evaporator at 65° C., and dried at 65° C. to obtain a black powder. The above black powder was ground, weighed, and placed in a quartz boat, then transferred to a tube furnace, programmed to heat up to 120°C at a rate of 5°C min ^-1 under _N2 atmosphere, and treated at this temperature for 0.5h , and then the temperature was programmed to 200°C at a rate of 5°C min ^-1 , a mixture of H ₂ and N ₂ with a volume fraction of 5% was passed, and the constant temperature heat treatment was performed for 2 hours to obtain the target product 20% Pd/C-200 electrocatalyst.

Comparative Example 3: 20% Pd/C-300 (20% means that the mass content of the active component Pd is 20%, -300 means that the reduction temperature is 300°C)

First, 80 mg of Vulcan XC-72 carbon black was ultrasonically dispersed in 30 mL of absolute ethanol, and then 30 mL of an aqueous solution containing 2.56 mL of Pd(NO ₃ ) ₂ with a mass fraction of 7.8 mg/mL was added. The above solution was impregnated and stirred at room temperature for 6 h, and then the solvent was removed using a rotary evaporator at 65° C., and dried at 65° C. to obtain a black powder. The above black powder was ground, weighed, and placed in a quartz boat, then transferred to a tube furnace, programmed to heat up to 120°C at a rate of 5°C min ^-1 under _N2 atmosphere, and treated at this temperature for 0.5h , and then the temperature was programmed to 300°C at a rate of 5°C min ^-1 , a mixture of H ₂ and N ₂ with a volume fraction of 5% was passed, and a constant temperature heat treatment was performed for 2 hours to obtain the target product 20% Pd/C-300 electrocatalyst.

Comparative Example 4: 20% Pd/C-400 (20% means that the mass content of the active component Pd is 20%, -400 means that the reduction temperature is 400°C)

First, 80 mg of Vulcan XC-72 carbon black was ultrasonically dispersed in 30 mL of absolute ethanol, and then 30 mL of an aqueous solution containing 2.56 mL of Pd(NO ₃ ) ₂ with a mass fraction of 7.8 mg/mL was added. The above solution was impregnated and stirred at room temperature for 6 h, and then the solvent was removed using a rotary evaporator at 65° C., and dried at 65° C. to obtain a black powder. The above black powder was ground, weighed, and placed in a quartz boat, then transferred to a tube furnace, programmed to heat up to 120°C at a rate of 5°C min ^-1 under _N2 atmosphere, and treated at this temperature for 0.5h , and then the temperature was programmed to 400°C at a rate of 5°C min ^-1 , a mixture of H ₂ and N ₂ with a volume fraction of 5% was passed, and the constant temperature heat treatment was performed for 2 hours to obtain the target product 20% Pd/C-400 electrocatalyst.

Comparative Example 5: 20% Pd/C-500 (20% means that the mass content of the active component Pd is 20%, -500 means that the reduction temperature is 500°C)

First, 80 mg of Vulcan XC-72 carbon black was ultrasonically dispersed in 30 mL of absolute ethanol, and then 30 mL of an aqueous solution containing 2.56 mL of Pd(NO ₃ ) ₂ with a mass fraction of 7.8 mg/mL was added. The above solution was impregnated and stirred at room temperature for 6 hours, and then the solvent was removed using a rotary evaporator at 65°C, and dried at 65°C to obtain a black powder of Pd(NO ₃ ) ₂ /C. The above black powder was ground, weighed, and placed in a quartz boat, then transferred to a tube furnace, programmed to heat up to 120°C at a rate of 5°C min ^-1 under _N2 atmosphere, and treated at this temperature for 0.5h , and then the temperature was programmed to 500°C at a rate of 5°C min ^-1 , a mixture of H ₂ and N ₂ with a volume fraction of 5% was passed, and the constant temperature heat treatment was carried out for 2 hours to obtain the target product 20% Pd/C-500 electrocatalyst.

Comparative example 6: 20%Ag/C-150 (20% means that the mass content of the active component Ag is 20%, and -150 means that the reduction temperature is 150°C)

First, 80 mg of Vulcan XC-72 carbon black was ultrasonically dispersed in 30 mL of absolute ethanol, and then 30 _mL of an aqueous solution containing 31.5 mg of AgNO was added. The above solution was impregnated and stirred at room temperature for 6 hours, and then the solvent was removed using a rotary evaporator at 65°C, and dried at 65°C to obtain black powder AgNO ₃ /C. The above black powder was ground, weighed, and placed in a quartz boat, then transferred to a tube furnace, programmed to heat up to 120°C at a rate of 5°C min ^-1 under _N2 atmosphere, and treated at this temperature for 0.5h , and then the temperature was programmed to 150°C at a rate of 5°C min ^-1 , a mixture of H ₂ and N ₂ with a volume fraction of 5% was passed, and the constant temperature heat treatment was carried out for 2 hours to obtain the target product 20% Ag/C-150 electrocatalyst.

Comparative Example 7: 20%Ag/C-500 (20% means that the mass content of the active component Ag is 20%, and -500 means that the reduction temperature is 500°C)

First, 80 mg of Vulcan XC-72 carbon black was ultrasonically dispersed in 30 mL of absolute ethanol, and then 30 _mL of an aqueous solution containing 31.5 mg of AgNO was added. The above solution was impregnated and stirred at room temperature for 6 hours, and then the solvent was removed using a rotary evaporator to obtain black powder AgNO ₃ /C. The above black powder was ground, weighed, and placed in a quartz boat, then transferred to a tube furnace, programmed to heat up to 120°C at a rate of 5°C min ^-1 under _N2 atmosphere, and treated at this temperature for 0.5h , and then the temperature was programmed to 500°C at a rate of 5°C min ^-1 , a mixture of H ₂ and N ₂ with a volume fraction of 5% was passed, and the constant temperature heat treatment was performed for 2 hours to obtain the target product 20% Ag/C-500 electrocatalyst.

FIG. 1 is the XRD spectrum of the samples prepared according to Comparative Examples 1, 3, 4, and 5. As can be seen from the PCPDF standard card below Figure 1, the samples prepared in Examples 1, 3, 4, and 5 all have the characteristic peaks of Pd, and 39, 46, 68 and 82° can be assigned to Pd's (111) respectively , (200), (220), and (311) diffraction peaks. The particle sizes of Pd in Examples 1, 3, 4, and 5 were calculated by the Scherrer formula to be 7.2, 8.7, 10.1, and 11.6 nn, respectively.

Figure 2 is the XRD spectrum of samples prepared according to Comparative Examples 5 and 6 and Examples 1, 2, 3, 4 and 9. As can be seen from the PCPDF standard card at the bottom of Fig. 2, the samples prepared in Comparative Examples 5 and 6 all have characteristic peaks of Pd and Ag, and 39, 46, 68 and 82° can be attributed to (111) and (200) of Pd respectively. ), (220), and (311) crystal planes, while 38, 44, 64, and 77° are attributed to Ag’s (111), (200), (220), and (311) crystal planes peak. In Examples 1 and 2, as the atomic ratio of PdAg metal decreases, the positions of the peaks move regularly, indicating that a PdAg alloy is formed. In Examples 3, 4, and 9, with the increase of the Ag content, the characteristic peaks of Pd and Ag appeared respectively, indicating that Ag was precipitated from the PdAg alloy. The particle diameters of PdAg in Comparative Examples 5 and 6 and Examples 1, 2, 3, 4 and 9 were calculated by the Scherrer formula to be 9.5, 27.8 and 6.8, 6.3, 5.2, 5.2 and 5.1 nm, respectively.

Fig. 3 is an XRD spectrum of samples prepared according to Examples 5-9. Comparing the PCPDF standard card at the bottom of Figure 3, it can be seen that the peak positions of Examples 5-9 are between the characteristic peaks of Pd and Ag, indicating that each example forms a PdAg alloy. The particle diameters of the alloys in Examples 5-9 were calculated by the Scherrer formula to be 3.4, 3.8, 3.9, 4.1 and 5.2 nm, respectively.

Fig. 4 is the CV graph of the samples prepared according to Comparative Examples 1-5 in _N2 saturated 1.0M NaOH electrolyte. According to the reduction peak area of PdO in the negative sweep process, the electrochemical specific surface areas of Comparative Examples 1-5 were 4.39, 4.16, 2.82, 2.61 and 2.10 cm ^-2 , indicating that the electrochemical specific surface areas gradually decreased with the increase of the reduction temperature. Small.

Fig. 5 is a CV diagram of samples prepared according to Comparative Examples 1-5 in N ₂ saturated 1.0M NaOH+1.0MCH ₃ CH ₂ OH electrolyte. It can be seen from the figure that the onset potentials of the comparative examples are the same, and the EOR current density of the comparative examples 1-5 increases gradually with the increase of the heat treatment temperature.

Fig. 6 is the CV diagram of samples prepared according to Comparative Examples 5, 7 and Examples 1, 2, 3, 4, 9 in N ₂ saturated 1.0M NaOH electrolyte. In Comparative Example 5, the peak corresponding to -0.8 to 0.5 V is the hydrogen absorption and desorption peak, and the peak corresponding to -0.4 to 0 V is the reduction peak of PdO _x during the negative sweep process. In Comparative Example 7, the peak corresponding to 0.1 to 0.3 V is the reduction peak of AgO _x . In Examples 1, 2, 3, 4, and 9, the adsorption and desorption peaks of hydrogen were suppressed to varying degrees, and there was no reduction peak of AgO _x . Combined with the XRD results, it can be known that PdAg formed an alloy in the examples.

Fig. 7 is a CV diagram of samples prepared according to Comparative Examples 5 and 7 and Examples 1, 2, 3, 4 and 9 in N ₂ saturated 1.0M NaOH+1.0M CH ₃ CH ₂ OH electrolyte. It can be seen from the figure that Comparative Example 7 has no catalytic activity for ethanol oxidation in alkaline medium, which is the same as the result reported in the literature. The catalytic activities of Examples 1, 2, 3, 4, and 9 to catalyze the oxidation of ethanol are all higher than those of Comparative Example 5, and the catalytic activities of Examples 2 and 9 are higher.

Fig. 8 is a CV diagram of samples prepared according to Examples 5-9 in N ₂ saturated 1.0M NaOH+1.0MCH ₃ CH ₂ OH electrolyte. It can be seen from the figure that when the PdAg atomic ratio is the same, the heat treatment temperature increases, and the activity of catalytic ethanol oxidation increases. Combined with the XRD results, it can be seen that the lattice constants of Examples 5-9 are the same, and the particle size gradually increases, indicating that the ethanol oxidation process in alkaline media requires a suitable catalyst particle size to meet the adsorption and desorption requirements of ethanol and intermediate products during the reaction process.

Claims (7)

1. a preparation method of Pd-Ag/C catalyst, comprises the following steps, is characterized in that: 1) Dispersion of the carbon carrier: Mix the carbon carrier with absolute ethanol, stir to make the carbon carrier evenly disperse in the ethanol to form a slurry; 2) Preparation of impregnation solution: Pd(NO ₃ ) ₂ and AgNO ₃ are mixed and dissolved in deionized water to form a solution, and the solution is added dropwise or poured into the container containing the carbon carrier slurry in step (1); Or dissolve Pd(NO ₃ ) ₂ and AgNO ₃ in deionized water to form solutions, and follow the order of Pd(NO ₃ ) ₂ solution first and then AgNO ₃ solution or first AgNO ₃ solution and then Pd(NO ₃ ) ₂ solution. Add drop by drop or pour in the container that is filled with carbon carrier slurry in step (1); The volume of deionized water in the immersion system is 0.5-1.5 times the volume of ethanol; immersion time ≥ 3h; 3) Preparation of Pd-Ag/C catalyst: a. the soaking liquid obtained in the above-mentioned steps (2) is evaporated to dryness; b. Dry the evaporated product obtained in the above step (3)a at 50-85°C for ≥5h to obtain a black powder; c. Put the black powder obtained in the above steps in a tube furnace and process it under an inert gas atmosphere. Heat treatment for 20-60min, then program the temperature to 150-700℃ at a rate of 1-10℃/min; d. Keep the final temperature in the above steps, feed the mixed gas of _H2 and inert gas with a volume fraction of 1-15% in the tube furnace, after heat treatment for 1-3h, wash and dry the black powder to obtain the target The product is a Pd-Ag/C catalyst, the active components in the catalyst are Pd and Ag, the total mass content of the active components in the catalyst is 1-30%, and the mass of Ag is not more than 25% of the Pd content. 2. The preparation method of the Pd-Ag/C catalyst as claimed in claim 1, characterized in that: the ratio of the carbon carrier to absolute ethanol is that the volume of absolute ethanol added to every 20 mg of carbon carrier is 5-40 mL. the 3. the preparation method of Pd-Ag/C catalyst as claimed in claim 1 is characterized in that: the Pd(NO ₃ ) ₂ mass concentration is 0.02mg/ mL to 7.8mg/mL, the mass concentration of AgNO ₃ is 0.005mg/mL to 1.95mg/mL. 4. the preparation method of Pd-Ag/C catalyst as claimed in claim 1, is characterized in that: Put the black powder obtained in the above step (3)b into a quartz or ceramic vessel after being ground and weighed; then put it into a tube furnace. the 5. the preparation method of Pd-Ag/C catalyst as claimed in claim 1, is characterized in that: In the above step (3)a, the impregnating liquid obtained in the above step (2) is rotary evaporated to dryness at 30-70°C. the 6. the preparation method of Pd-Ag/C catalyst as claimed in claim 1, is characterized in that: The carbon carrier is: one or a mixture of two or more of XC-72R, BP2000, acetylene black, carbon nanotubes, and graphite oxide; The inert atmosphere is one or a mixture of nitrogen, argon, and helium. the 7. the preparation method of Pd-Ag/C catalyst as claimed in claim 1, is characterized in that: The impregnation process is carried out under the condition of magnetic stirring at 0-50° C., and the impregnation is ≥3 hours. the

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