CN100398211C - A kind of core-shell catalyst for fuel cell and preparation method thereof - Google Patents

Abstract

The present invention provides a nucleocapsid catalyst for fuel cells and the preparing method thereof. The present invention is characterized by the controllability of the size of the catalyst and the thickness of a catalyst layer with catalyzing effects. The metallic activity of metal with low standard electrode electric potential is higher than that of metal with high standard electrode electric potential, and thus, the simple substances of ions of the metal with high standard electrode potential are easily separated. Firstly, nanometer particles of metal with low standard electrode electric potential are prepared, and metal with high standard electrode electric potential is separated by the nanometer particles; the amount of the separated metal is controlled less than the amount required by a replacement reaction theory; thus, the separated metal is coated on the surface of the nanometer particle of the metal with low standard electrode electric potential to obtain the nucleocapsid catalyst. The nucleocapsid catalyst with various thicknesses of catalyst layers can be obtained through adjusting the dose ratio of the two kinds of metal; the particle diameter of the nucleocapsid catalyst can be controlled through controlling the particle diameter of the prepared nanometer particle of the metal with high metal activity. The nucleocapsid catalyst prepared by the method has the advantages of large active specific surface area and high catalyzing efficiency.

Description

A kind of core-shell catalyst for fuel cell and preparation method thereof

technical field

The invention belongs to a core-shell catalyst for a fuel cell and a preparation method thereof

Background technique

Nano-sized unsupported metal particles are prone to agglomeration, resulting in a decrease in specific surface area. Therefore, catalysts used in fuel cells are generally supported noble metal catalysts, such as carbon-supported platinum, ruthenium, and the like. Due to the scarcity and high price of these noble metal resources, it is necessary to adopt appropriate preparation methods and production processes to reduce the particle size of the catalyst, make its particle size distribution uniform, and increase the dispersion of the catalyst to prevent catalyst agglomeration, thereby improving the activity and performance of the catalyst. utilization rate. Many researchers at home and abroad have tried various methods to prepare supported noble metal catalysts.

US3,992,331 introduces a method for preparing a highly dispersed active carbon supported platinum catalyst. The method first converts chloroplatinic acid (H2PtCl6) into sodium platinum sulfite (Na6[Pt(SO ₃ ) ₄ ]), then converts sodium platinum sulfite into hydrogen form, heats and boils in air to release excess sulfurous acid Sulfate ions are dried at a certain temperature to obtain platinum black colloids, and carbon supports are added to absorb the platinum colloids to make platinum catalysts of 1.5-2.5 nanometers. In the method, chloride ions are replaced by sulfite radicals, and the degradation of the catalytic performance of the catalyst caused by trace amounts of chloride ions is eliminated. However, the method has complicated operation procedures and high preparation costs.

US5,641,723 introduces a process for preparing supported metal catalysts by colloidal method. This method uses NR ₄ BR ₃ H to reduce metal salts in tetrahydrofuran (THF), and prepares nanoscale metal colloids with uniform particle size distribution protected by various quaternary ammonium salts, and then adds various carriers to absorb the prepared metal colloids to obtain supported catalyst. The method operates under anhydrous and oxygen-free conditions, uses large amounts of toxic solvents, and leaves a large amount of waste residues.

US5,068,161 introduces a method for preparing supported metal catalysts by impregnation reduction method. In this method, the chloroplatinic acid solution is added to the carbon powder adjusted to be alkaline with NaHCO ₃ , and after a large amount of CO ₂ gas is released, it is dried by adding formaldehyde, formic acid, hydrazine hydrate and other reducing agents or directly filtered, and then passed into N ₂ / The H ₂ mixed gas is reduced at high temperature to obtain a supported Pt/C catalyst. [CN99112700.5, CN02118282.5] also introduced a method for preparing supported catalyst by impregnation reduction method, the difference is that the method is completed in an organic solvent or a mixed solvent. The platinum metal particles prepared by the above impregnation reduction method have uneven particle size and wide distribution, especially at high loads.

Amine K, et a1.J.Chen.Soc.Fara.Trans, 1995, 91:4451 introduced a method for preparing supported catalysts by ion exchange. In this method, the carrier carbon is treated with an oxidant, so that there are many negatively charged functional groups on the surface of the carbon, and the positively charged platinum ammonium complex ion [Pt(NH ₃ ) ₄ ²⁺ ] The negatively charged functional groups are introduced into the carbon surface, and then platinum particles are reduced with a reducing agent to obtain a supported Pt/C catalyst. Due to the limited number of negatively charged functional groups introduced on the carbon surface, it is difficult to achieve a platinum loading of more than 5%.

Wu Shihua et al., Petrochemical Industry, 187: 361 introduced vacuum sputtering and metal vapor deposition methods to prepare catalysts, but these two methods require very high equipment and are not suitable for mass production.

Contents of the invention

The object of the present invention is to provide a fuel cell core-shell catalyst with large specific surface area, good dispersion, high catalytic activity and high utilization rate and its preparation method.

In order to achieve the above purpose, metals with low standard electrode potential are used, and their metal activity is higher than that of metals with high standard electrode potential, so that metal ions with high standard electrode potential can be easily replaced and precipitated as simple substances. First, prepare metal nanoparticles with low standard electrode potential, use them to replace metals with high standard electrode potential, and control the amount of replaced metal to be less than the amount required by the replacement reaction theory, so as to obtain the replaced metal coated on the standard Core-shell catalysts on the surface of metal nanoparticles with low electrode potential. By adjusting the dose ratio of the two metals, core-shell catalysts with various thicknesses of the catalytic layer can be obtained; by controlling the particle size of the prepared metal nanoparticles with high metal activity, the particle size of the core-shell structure catalyst can be controlled.

Technical scheme of the present invention is:

A core-shell catalyst is characterized in that the catalyst is a core-shell structure catalyst in which a metal with low metal activity is wrapped on the surface of a metal nanoparticle with high metal activity. It is prepared by the following method, and the preparation steps are:

Step 1. Configure a mixed solution, add a surfactant to the deionized water solvent, stir, and add a metal water-soluble compound with high metal activity at the same time to form a mixed solution. The content of the metal in the mixed solution is 0.001 to 1 mol/liter. The content of the surfactant is 0.001 to 1 mole/liter, wherein the molar ratio of the surfactant to the metal is 0.1 to 10:1, and the solvent is deionized water with a conductivity > 18 megohms;

Step 2, adding a reducing agent 1 to 10 times the number of moles of the metal to the mixed solution in step 1, stirring, and introducing _H2 for protection, so as to obtain a nano-metal solution with high metal activity;

Step 3, adding the metal solution with low metal activity to the nano-metal solution with high metal activity prepared in step 2 while stirring, and stirring for 0.5 to 20 hours to obtain the metal with low metal activity wrapped on the surface of the metal nanoparticles with high metal activity The core-shell structure catalyst solution;

Step 4. Suction filter the core-shell structure catalyst solution obtained in step 3, wash with deionized water for 3 to 5 times, and vacuum-dry at 60-90°C to obtain an unsupported core-shell catalyst; or obtain a core-shell structure in step 3 Add the carrier into the catalyst solution, stir vigorously for 10-25 hours, filter with suction, wash with deionized water for 3-5 times, and dry in vacuum at 60-90°C to obtain a supported core-shell catalyst, wherein the mass ratio of the carrier to the metal is 10: 1 ~ 100.

Wherein, the metal water-soluble compounds with high metal activity include water-soluble halides, sulfates, nitrates and phosphates of Fe, Co, Ni, Cu, Mn, Cr, Ti, V and Mo metals.

The surfactants include sulfonate (the general formula is R-SO ₃ Na, the carbon number in R is between 8 and 20), sulfate salt (the general formula is ROSO ₃ M, where M is Na, K , N(CH ₂ CH ₂ OH) ₃ , the number of carbons in the carbon chain is 8-18), amine salts (divided into primary, secondary, tertiary and quaternary ammonium salts according to the number of organic substituents on the nitrogen atom), citric acid and Its salt surfactant, amino acid type and imidazoline type amphoteric surfactant, polyethylene glycol type, polyol type and alkylthiol type nonionic surfactant.

The reducing agent is NaBH ₄ or N ₂ H ₂ ·H ₂ O.

The metal solution with low metal activity includes water-soluble sulfates, nitrates, phosphates, complexes, halides, carbonyl compounds, hydrohalic acids of Pt, Pd, Ru, Rh, Ir, Os, Au, Ag and salt solution.

The carrier of the supported catalyst is a material with high specific surface area, good conductivity and good stability, including: graphite, carbon black, carbon nanotubes, carbon fibers, C-SBA-15, fullerene, conductive polymer , Al ₂ O ₃ , SiO ₂ , MgO, TiO ₂ and molecular sieves.

The thickness of the metal cladding layer with low metal activity on the surface of the core-shell structure catalyst is controlled by adjusting the dosage ratio of the metal with high metal activity to the metal with low metal activity; when the dosage ratio of the metal with high metal activity to the metal with low metal activity When it is large, the thickness of the metal cladding layer with low metal activity on the surface of the core-shell structure catalyst takes a small value; the particle size of the core-shell structure catalyst is controlled by the particle size of the prepared metal nanoparticles with high metal activity, when the metal with high metal activity When the particle size of the nanoparticles is small, the particle size of the core-shell structure catalyst takes a small value.

The preparation method of core-shell catalyst of the present invention, it comprises the steps:

Step 1. Configure a mixed solution, add a surfactant to the deionized water solvent, stir, and add a metal water-soluble compound with high metal activity at the same time to form a mixed solution. The content of the metal in the mixed solution is 0.001 to 1 mol/liter. The content of the surfactant is 0.001 to 1 mole/liter, wherein the molar ratio of the surfactant to the metal is 0.1 to 10:1, and the solvent is deionized water with a conductivity > 18 megohms;

Step 2, adding a reducing agent 1 to 10 times the number of moles of the metal to the mixed solution in step 1, stirring, and introducing _H2 for protection, so as to obtain a nano-metal solution with high metal activity;

Step 3, adding the metal solution with low metal activity to the nano-metal solution with high metal activity prepared in step 2 while stirring, and stirring for 0.5 to 20 hours to obtain the metal with low metal activity wrapped on the surface of the metal nanoparticles with high metal activity The core-shell structure catalyst solution;

Step 4. Suction filter the core-shell structure catalyst solution obtained in step 3, wash with deionized water for 3 to 5 times, and vacuum-dry at 60-90°C to obtain an unsupported core-shell catalyst; or obtain a core-shell structure in step 3 Add the carrier into the catalyst solution, stir vigorously for 10-25 hours, filter with suction, wash with deionized water for 3-5 times, and dry in vacuum at 60-90°C to obtain a supported core-shell catalyst, wherein the mass ratio of the carrier to the metal is 10:1～100;

The metal water-soluble compounds with high metal activity include Fe, Co, Ni, Cu, Mn, Cr, Ti, V and Mo metal water-soluble halides, sulfates, nitrates and phosphates; the surface active The agent includes the general formula R-SO ₃ Na, sulfonate with carbon number between 8 and 20 in R, the general formula ROSO ₃ M, where M is Na, K, N(CH ₂ CH ₂ OH) ₃ , sulfate salt, amine salt, citric acid and its salt surfactants with carbon number of 8-18 in the carbon chain, amino acid type and imidazoline type amphoteric surfactants, polyethylene glycol type, polyol type and alkyl Mercaptan nonionic surfactant; the reducing agent is NaBH ₄ or N ₂ H ₂ ·H ₂ O; the metal solution with low activity includes Pt, Pd, Ru, Rh, Ir, Os, Au, Ag water-soluble sulfates, nitrates, phosphates, complexes, halides, carbonyl compounds, hydrohalic acids and salt solutions; the carrier of the supported catalyst is graphite, carbon black, carbon nanotubes, Carbon fiber, C-SBA-15, fullerene, conductive polymer, Al ₂ O ₃ , SiO ₂ , MgO, TiO ₂ or molecular sieve.

The feature of the present invention is to use the difference in metal activity to first prepare metal nanoparticles with high activity, and then replace the metal with low metal activity from its solution to obtain a core-shell structure in which the catalytic noble metal is wrapped on the surface of the base metal catalyst. Moreover, the thickness of the noble metal that plays a catalytic role is controlled by adjusting the dosage ratio of the two metals; the particle size of the core-shell catalyst is controlled by adjusting the particle size of the prepared metal nanoparticles with high metal activity. This core-shell catalyst can be used as an unsupported catalyst, or deposited on a carrier such as carbon powder or carbon nanotube as a supported catalyst. The invention can greatly increase the specific surface area of the noble metal that plays a catalytic role, and better play its catalytic role.

Description of drawings

Fig. 1 is the single cell polarization curve of embodiment 1 and comparative example 1;

Fig. 2 is the transmission electron microscope figure of embodiment 1 of the present invention;

Fig. 3 is the transmission electron microscope figure of embodiment 2 of the present invention;

Figure 1 shows that the fuel cell of the present invention has good output performance and high catalytic efficiency of the catalyst.

Detailed ways

The present invention will be further described below in conjunction with the embodiments and accompanying drawings.

Example 1

Take 500 ml of 0.05 mol/liter polydiallyldimethylammonium chloride, add 500 ml of 0.02 mol/liter nickel chloride solution, and stir for 3 minutes with an electric motor at a speed of 300 rpm. Add 15 ml of 0.1 mol/L NaBH ₄ , stir for 5 minutes, and pass through H ₂ for protection. 100 ml of 0.01 mol/L H ₂ PtCl ₆ solution was added, and electric stirring was performed at 500 rpm for 1 hour. Add 0.29 g of VulcanXC-72 carbon powder, electric stirring for 15 hours at 5000 rpm, filter and rinse with deionized water for 5 times, and vacuum dry at 80°C. The mass ratio of carbon to platinum in the prepared carbon-supported [nickel] (platinum) catalyst (the elements in the square brackets represent the core of the core-shell structure, and the elements in the brackets represent the shell of the core-shell structure) is 3:2. The transmission electron microscope image of the catalyst is shown in Fig. 2 .

Comparative example 1

Get platinum loading as quality 40%Pt/C catalyst (produced by Johnson Matthey company, the average particle diameter of catalytically active particle Pt is 3 nanometers, Pt loading is quality 40%) as anode and cathode catalyst, and take embodiment one The catalyst is used as the catalyst of the anode and the cathode to compare the performance of the single cell.

Cell assembly and performance testing. The carbon paper produced by E-TEK Company is used as the diffusion layer, and the carbon paper has been treated with 30% PTFE (polytetrafluoroethylene) in advance and has a thickness of 100 microns. The catalyst was coated onto hydrophobic carbon paper with a platinum loading of 0.4 mg/cm ² for both the anode and cathode. The Nafion212 membrane produced by DuPont Company is used as the proton exchange membrane, and the Nafion212 membrane is immersed in a weight concentration of 5% H ₂ O ₂ , heat-treated at 80° C. for 1 hour, and rinsed with deionized water for 3 times; then immersed in 0.5 mol/liter of Heat treatment in H ₂ SO ₄ solution at 80°C for 1 hour; then heat treatment in deionized water at 80°C for 1 hour, during which deionized water was replaced 3 times. Then the treated Nafion212 film was sandwiched between carbon paper brushed with catalyst, and hot-pressed at 125°C for 90 seconds at a pressure of 0.2 MPa. A graphite plate with parallel grooves on one side is used as the collector plate, and the end plate is a gold-plated stainless steel plate. The operating conditions are: P _CO2 =P _H2 =0 MPa, the battery temperature is 60°C, the anode is 100% humidified, and the humidification temperature is 70°C.

The single-cell polarization curves of Example 1 and Comparative Example 1 are shown in Fig. 1, indicating that the fuel cell of the present invention has good output performance and high catalytic efficiency of the catalyst.

Example 2

Take 500 ml of 0.02 mol/L sodium citrate, add 500 ml of 0.01 mol/L cobalt chloride solution, and stir electrically for 5 minutes at a speed of 500 rpm. Add 15 ml of 0.1 mol/L NaBH ₄ , stir for 5 minutes, and pass through H ₂ for protection. Add 100 ml of 0.01 mol/L H ₂ PtCl ₆ solution, stir electrically for 1 hour at 500 rpm, filter and rinse with deionized water 5 times, and vacuum dry at 60°C. The prepared [cobalt] (platinum) catalyst. The transmission electron microscope picture of its catalyst is shown in Fig. 3

Example 3

Take 500 ml of 0.04 mol/liter sodium dodecylsulfonate solution, add 500 ml of 0.01 mol/liter ferric sulfate solution, and stir for 4 minutes with a rotating speed of 400 rpm. Add 40 ml of 0.1 mol/L N ₂ H ₂ ·H ₂ O, stir for 5 minutes, and pass through H ₂ for protection. Add 100 ml of 0.01 mol/L RuCl ₃ solution, and stir with electric motor at 500 rpm for 1 hour. Add 0.404 g of VulcanXC-72 carbon powder, electric stirring for 15 hours at 5000 rpm, filter and rinse with deionized water 5 times, and vacuum dry at 80°C. The mass ratio of carbon to ruthenium in the prepared carbon-supported [iron] (ruthenium) catalyst is 4:1.

Claims (3)

1. a preparation method of core-shell catalyst, is characterized in that, comprises the steps: Step 1. Configure a mixed solution, add a surfactant to the deionized water solvent, stir, and add a metal water-soluble compound with high metal activity at the same time to form a mixed solution. The content of the metal in the mixed solution is 0.001 to 1 mol/liter. The content of the surfactant is 0.001-1 mol/liter, wherein the molar ratio of the surfactant to the metal is 0.1-10:1, and the solvent is deionized water with a conductivity > 18 megohms; Step 2, adding a reducing agent 1 to 10 times the number of moles of the metal to the mixed solution in step 1, stirring, and introducing H2 protection to prepare a nano-metal solution with high metal activity; Step 3, adding the metal solution with low metal activity to the nano-metal solution with high metal activity prepared in step 2 while stirring, and stirring for 0.5 to 20 hours to obtain the metal with low metal activity wrapped on the surface of the metal nanoparticles with high metal activity The core-shell structure catalyst solution; Step 4. Suction filter the core-shell structure catalyst solution obtained in step 3, wash with deionized water for 3 to 5 times, and vacuum-dry at 60-90°C to obtain an unsupported core-shell catalyst; or obtain a core-shell structure in step 3 Add the carrier into the catalyst solution, stir vigorously for 10-25 hours, filter with suction, wash with deionized water for 3-5 times, and dry in vacuum at 60-90°C to obtain a supported core-shell catalyst, wherein the mass ratio of the carrier to the metal is 10:1~100; Wherein, the metal water-soluble compounds with high metal activity include Fe, Co and Ni, Cu, Mn, Cr, Ti, V and Mo metal water-soluble halides, sulfates, nitrates and phosphates; Surfactants include the general formula R-SO ₃ Na, sulfonates with carbon number between 8 and 20 in R, the general formula ROSO ₃ M, where M is Na, K, N(CH ₂ CH ₂ OH ) ₃ , surfactants of sulfate fatty acid salts, amine salts, citric acid and their salts with carbon number of 8-18 in the carbon chain, amino acid type and imidazoline type amphoteric surfactants, polyethylene glycol type, polyol type and Alkylthiol type nonionic surfactant; the reducing agent is NaBH ₄ or N ₂ H ₂ ·H ₂ O; the metal solution with low activity includes Pt, Pd, Ru, Rh, Ir, Os, Water-soluble sulfates, nitrates, phosphates, complexes, halides, carbonyl compounds, hydrohalic acids and salt solutions of Au and Ag; the carrier of the supported catalyst is graphite, carbon black, carbon nano tube, carbon fiber, C-SBA-15, fullerene, conductive polymer, Al ₂ O ₃ , SiO ₂ , MgO, TiO ₂ or molecular sieve. 2. the preparation method of a kind of core-shell catalyst as claimed in claim 1 is characterized in that the thickness of the metal coating layer with low metal activity on the surface of the core-shell structure catalyst is adjusted by adjusting the metal with high metal activity and the low metal activity. The dose ratio control of the metal; when the dose ratio of the metal with high metal activity to the metal with low metal activity is large, the thickness of the metal cladding layer with low metal activity on the surface of the core-shell structure catalyst takes a small value; the particle size of the core-shell structure catalyst is determined by The particle size of the prepared metal nanoparticles with high metal activity is controlled. When the particle size of the metal nanoparticles with high metal activity is small, the particle size of the core-shell structure catalyst is taken as a small value. 3. The core-shell catalyst prepared by the preparation method of claim 1 or 2, characterized in that the catalyst is a core-shell structure catalyst in which a metal with low metal activity is wrapped on the surface of a metal nanoparticle with high metal activity, wherein the metal activity High metals include Fe, Co, Ni, Cu, Mn, Cr, Ti, V and Mo; said metals with low metal activity include Pt, Pd, Ru, Rh, Ir, Os, Au and Ag.

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