阅读说明：本技术 一种燃料电池用双元或多元贵金属催化剂的制备方法 (Preparation method of binary or multi-element noble metal catalyst for fuel cell ) 是由 张义煌 张明 华秋茹 陈杰 李刚 于 2020-05-15 设计创作，主要内容包括：本发明属于燃料电池技术领域,特别涉及到一种燃料电池用双元或多元贵金属催化剂的制备方法。本发明在贵金属中引入一种或多种过渡金属组分并使贵金属与过渡金属合金化,合金化的阴极氧还原活性比单组分贵金属氧还原活性要高,且能够降低贵金属的载量；采用球形多孔活性炭,其较大的比表面积可使催化剂暴露更多活性位点,所制备的纳米合金颗粒都集中在碳载体的表面,能够提升催化剂的利用率。在制备过程中,一种或多种前驱体溶液形成溶胶凝胶,大分子柠檬酸与金属离子络合形成一个整体,既可避免纳米合金颗粒嵌入活性炭的内部孔隙,也可以提升纳米合金颗粒的合金化,提高催化剂的性能。(The invention belongs to the technical field of fuel cells, and particularly relates to a preparation method of a binary or multi-element noble metal catalyst for a fuel cell. One or more transition metal components are introduced into the noble metal, the noble metal and the transition metal are alloyed, the oxygen reduction activity of the alloyed cathode is higher than that of a single-component noble metal, and the loading capacity of the noble metal can be reduced; the spherical porous activated carbon is adopted, the catalyst can expose more active sites due to the large specific surface area of the spherical porous activated carbon, and the prepared nano alloy particles are concentrated on the surface of the carbon carrier, so that the utilization rate of the catalyst can be improved. In the preparation process, one or more precursor solutions form sol-gel, and macromolecular citric acid and metal ions are complexed to form a whole, so that not only can the nano alloy particles be prevented from being embedded into the internal pores of the activated carbon, but also the alloying of the nano alloy particles can be improved, and the performance of the catalyst is improved.)

1. A method for preparing a binary or multi-element noble metal catalyst for a fuel cell, comprising the steps of:

(1) dissolving porous activated carbon, a noble metal precursor and a transition metal precursor in ultrapure water, uniformly stirring to obtain a mixed solution, adding a citric acid solution into the mixed solution while stirring, and then adjusting the pH of the mixed solution to 7.2-10.8 to form sol;

(2) heating the sol in a heating device at 90-120 deg.C for 30-120min under stirring until the sol is converted into viscous gel;

(3) putting a certain amount of gel into a tube furnace to continuously carry out two-stage heat treatment, wherein the citric acid is removed in the first stage, and the reduction alloying treatment is carried out in the second stage;

(4) and after the second stage of heat treatment is finished, cooling to room temperature, adding a proper amount of inorganic acid solution into the gel to immerse the sample, standing the sample for a period of time at room temperature, filtering and cleaning the sample by using a large amount of ultrapure water after standing, taking the filtrate every time of filtering and cleaning, measuring the conductivity until the conductivity of the filtrate is reduced to below 10uS/cm, and finally drying the sample in a drying oven to obtain the carbon-supported binary or multi-element alloy catalyst.

2. The method for preparing a binary or multiple noble metal catalyst for a fuel cell according to claim 1, wherein the activated carbon in the step (1) is spherical porous activated carbon, and the molar ratio of citric acid to total metal ions is 1:20 to 10: 1.

3. The method for preparing a binary or multiple noble metal catalyst for a fuel cell according to claim 1, wherein the noble metal precursor in the step (1) is one or more of Pt, Pd, Ru, Os, Ir, Rh, or Re, and the mass content of the noble metal is 0.1% to 90%.

4. The method for preparing a binary or multiple noble metal catalyst for a fuel cell according to claim 1, wherein the transition metal precursor in the step (1) is one or more of Ti, Mn, Cr, Fe, Co, Ni, Cu, Zn, Sn, or Ce.

5. The method for preparing a binary or multiple noble metal catalyst for a fuel cell according to claim 1, wherein the inorganic acid in the step (2) is a nitric acid, sulfuric acid or hydrochloric acid solution having a concentration of 0.1 to 2 mol/L.

6. The method for preparing a binary or multiple noble metal catalyst for a fuel cell according to claim 1, wherein the heat treatment in the step (3) comprises the steps of:

first-stage heat treatment: heat-treating the gel at the temperature of 120-280 ℃ for 0.5-2h to remove the citric acid;

second-stage heat treatment: reducing noble metal and transition metal simultaneously in reducing atmosphere at 150-1200 deg.c for 20-240 min.

7. The method of preparing a binary or multiple noble metal catalyst for a fuel cell according to claim 1, wherein the noble metal and/or the transition metal in the noble metal catalyst has a particle size of 0.5 to 8 nm.

8. The method of preparing a binary or multiple noble metal catalyst for a fuel cell according to claim 1, wherein the noble metal and/or the transition metal in the noble metal catalyst has a particle size of 1 to 5 nm.

9. The method for producing a binary or multiple noble metal catalyst for a fuel cell according to claim 1, wherein the temperature is naturally lowered by switching to a reducing atmosphere after the first-stage heat treatment and switching to an inert atmosphere after the second-stage heat treatment.

Technical Field

The invention belongs to the technical field of fuel cells, and particularly relates to a preparation method of a binary or multi-element noble metal catalyst for a fuel cell.

Background

The supported noble metal catalyst for fuel cell has mature preparation process, and the supported metal is easy to disperse and the catalyst is easy to prepare. However, it is not easy to highly disperse the supported metal in the supported metal catalyst, especially in the bi-component and multi-component metal catalysts, which have a wider application range and are supported at a high load, and thus the utilization rate of the noble metal is not high.

The catalyst used in low temperature fuel cells such as Proton Exchange Membrane Fuel Cells (PEMFCs) and Direct Methanol Fuel Cells (DMFCs) is mainly a high-loading Pt catalyst or a Pt-based bi-component or multi-component catalyst, and the electrode catalyst is required to have a high noble metal loading, and the noble metal content is more than 10% -90% at a lower operating temperature (the operating temperature of these fuel cells is not more than 180 ℃) to ensure a certain reaction rate. However, noble metal resources are limited and expensive, and it is necessary to improve the utilization efficiency of noble metals, and the preparation of a nano-sized uniformly dispersed supported catalyst is absolutely necessary to promote the development of low-temperature fuel cells.

Because the highly conductive nano activated carbon is adopted, a large amount of noble metal catalyst particles filled in nano holes in the activated carbon do not participate in the electrochemical reaction of the fuel cell in the conventional impregnation method, and the utilization rate of the catalyst is greatly reduced.

For noble metal catalysts with high loading for other purposes, how to effectively improve the dispersion degree of noble metals so as to effectively improve the interaction between noble metals and transition metals, improve the activity of the catalyst and improve the utilization rate of noble metal resources is also a problem to be solved in the aspect of catalyst preparation.

Disclosure of Invention

The technical problem to be solved by the present invention is to provide a method for preparing a binary or multi-element noble metal catalyst for a fuel cell, aiming at the defects of the prior art. The preparation method of the invention forms gel by changing the composition of the solvent in the dispersion system, can effectively reduce the diffusion rate of the metal particles, prevent the metal particles from being polymerized with each other and being enlarged, and various kinds of metals are completely alloyed at lower temperature without annealing treatment at high temperature, and prevent the loss of due activity due to the growth of catalyst particles.

In order to solve the technical problems, the invention adopts the following technical scheme: a preparation method of a binary or multi-element noble metal catalyst for a fuel cell comprises the following steps:

(1) dissolving porous activated carbon, a noble metal precursor and a transition metal precursor in ultrapure water, uniformly stirring to obtain a mixed solution, adding a citric acid solution into the mixed solution while stirring, and then adjusting the pH of the mixed solution to 7.2-10.8 to form sol;

(2) heating the sol in a heating device at 90-120 deg.C for 30-120min under stirring until the sol is converted into viscous gel;

(3) putting a certain amount of gel into a tube furnace to continuously carry out two-stage heat treatment, wherein the citric acid is removed in the first stage, and the reduction alloying treatment is carried out in the second stage;

(4) and after the second stage of heat treatment is finished, cooling to room temperature, adding a proper amount of inorganic acid solution into the gel to immerse the sample, standing the sample for a period of time at room temperature, filtering and cleaning the sample by using a large amount of ultrapure water after standing, taking the filtrate every time of filtering and cleaning, measuring the conductivity until the conductivity of the filtrate is reduced to below 10uS/cm, and finally drying the sample in a drying oven to obtain the carbon-supported binary or multi-element alloy catalyst.

The active carbon in the step (1) is spherical porous active carbon, and the molar ratio of citric acid to total metal ions is 1:20-10: 1.

In the step (1), the precious metal precursor is one or more of Pt, Pd, Ru, Os, Ir, Rh or Re, and the mass content of the precious metal is 0.1-90%.

In the step (1), the transition metal precursor is one or more of Ti, Mn, Cr, Fe, Co, Ni, Cu, Zn, Sn or Ce.

The inorganic acid in the step (2) is nitric acid, sulfuric acid or hydrochloric acid solution with the concentration of 0.1-2 mol/L.

The heat treatment in the step (3) comprises the following steps:

first-stage heat treatment: heat-treating the gel at the temperature of 120-280 ℃ for 0.5-2h to remove the citric acid;

second-stage heat treatment: reducing noble metal and transition metal simultaneously in reducing atmosphere at 150-1200 deg.c for 20-240 min.

The particle size of the noble metal and/or the transition metal in the noble metal catalyst is 0.5-8 nm.

The particle size of the noble metal and/or the transition metal in the noble metal catalyst is 1-5 nanometers.

And after the first-stage heat treatment is finished, switching to a reducing atmosphere, and after the second-stage heat treatment is finished, switching to an inert atmosphere and naturally cooling.

Compared with the prior art, the invention has the following advantages:

(1) one or more transition metal components are introduced into the noble metal, the noble metal and the transition metal are alloyed, the oxygen reduction activity of the alloyed cathode is higher than that of single noble metal, and the loading capacity of the noble metal can be reduced;

(2) the spherical porous activated carbon is adopted, the catalyst can expose more active sites due to the large specific surface area of the spherical porous activated carbon, and the prepared nano alloy particles are concentrated on the surface of the carbon carrier, so that the utilization rate of the catalyst can be improved.

(3) In the preparation process, one or more precursor solutions form sol-gel, so that the nano alloy particles can be prevented from being embedded into the internal pores of the activated carbon, the alloying of the nano alloy particles can be improved, and the performance of the catalyst is improved.

(4) In the sol-gel stage, macromolecular citric acid and metal ions are complexed to form a whole, so that the metal ions can be effectively prevented from entering gaps of the spherical porous activated carbon, and the utilization rate of platinum is improved.

(5) In the alloying stage, the slightly strong adsorption capacity of platinum to oxygen-containing species can be reduced due to the existence of the transition metal, which is a key factor for improving the oxygen reduction performance of the binary or multicomponent alloy.

(6) In the treatment stage after the catalyst is acid-washed, the transition metal which does not participate in alloying can be removed to avoid the attack on a proton exchange membrane, and simultaneously, the acid-washing can also remove the transition metal on the surface of an active component, thereby being beneficial to the activity and the service life of the catalyst.

Drawings

Fig. 1 is a flow chart showing the preparation of a binary or multi-element noble metal catalyst for a fuel cell according to the present invention.

FIG. 2 is a comparison of the performance of the catalysts prepared in example 1 of the present invention and comparative example 1.

Detailed Description

The technical solution of the present invention will be further described with reference to specific examples.