CN111261886A - A non-precious metal-modified platinum-based catalyst for fuel cells and its preparation method and application - Google Patents

Abstract

The invention provides a platinum-based catalyst modified with a trace amount of non-precious metal and a preparation method thereof, and the catalyst can be used as a low-temperature fuel cell catalyst. The preparation method uses high-viscosity alcohol such as ethylene glycol, polyethylene glycol, glycerol, etc. as solvent and stabilizer, and reduces platinum and non-precious metals with strong reducing agents such as hydrazine hydrate, tetrabutyl borohydride, citric acid, ascorbic acid, etc. Precursor, combined with acid etching treatment to obtain supported ultra-fine platinum-based alloy nanoparticles containing trace amounts of non-precious metals and platinum shell structures. The preparation method adopted in the present invention is simple and effective, and is expected to realize mass production. In addition, based on the unique structural features of the obtained catalyst, including ultra-small catalyst particle size and uniform particle size distribution, micro-stabilized non-precious metal decoration, and several-layer Pt shell structure, it has excellent catalysis for the oxygen reduction reaction of fuel cell cathodes. The activity and cycle stability can effectively reduce the amount of platinum and have potential application prospects in low-temperature fuel cells.

Description

A kind of non-precious metal modified platinum-based catalyst for fuel cell and its preparation method and application

technical field

The invention belongs to the field of fuel cells, and in particular relates to a trace non-precious metal modified platinum-based catalyst for fuel cells.

Background technique

Proton exchange membrane fuel cell (PEMFC) has the advantages of high power density, high energy efficiency, fast start-up speed and low environmental pollution. It is an ideal clean energy and has broad application prospects in the fields of stationary power stations and transportation. However, the slow kinetic rate of the oxygen reduction reaction at the fuel cell cathode limits the performance of the fuel cell to a certain extent, so an efficient electrochemical catalyst is required to accelerate this process. The most widely used catalysts are carbon-supported Pt nanoparticle catalysts (Pt/C). However, as we all know, Pt, as a rare precious metal, has limited reserves on earth and is expensive, resulting in the high cost of fuel cells, which seriously hinders the commercial development of fuel cells. In addition, although Pt/C catalysts exhibit good activity for ORR, they usually exhibit insufficient stability under the high-potential operating conditions and acidic environments of practical PEMFCs. The commercialization of batteries has a very important role in promoting.

So far, people have improved the catalytic activity by alloying Pt with transition metals Fe, Co, Ni, etc., and achieved a reduction in the amount of Pt and the cost of fuel cells. For example, Chen et al. prepared Pt ₃ Ni nanocages catalyst by solvothermal reduction method, and its catalytic activity and stability were significantly improved compared with commercial Pt/C (Chen, C., et al.,. Science, 2014.343 (Chen, C., et al.,. Science, 2014.343 ( 6177):p.1339-43.). The Pt ₃ Co catalyst was prepared by the method of chemical reduction combined with heat treatment by Tanaka Precious Metal Industry, which can achieve a high power density about 1.5 times that of the Pt/C catalyst for fuel cells. Although the above-mentioned Pt alloy catalyst can improve the catalytic performance of oxygen reduction, its preparation process is complicated and energy consumption is high, which is not conducive to industrial production. In addition, under fuel cell conditions, the dissolution of transition metals can cause attenuation of catalyst activity and membrane degradation, resulting in a reduction in practical PEMFC performance. Therefore, it is urgent to explore a simple and effective method to prepare platinum-based alloy catalysts with high activity and high stability.

SUMMARY OF THE INVENTION

In view of the above technical problems, the present invention adopts a modified alcohol reduction method combined with acid etching pretreatment to prepare a trace amount of non-precious metal-modified Pt-based alloy catalyst, which can significantly improve catalytic activity and stability when used in fuel cells. The technical solution adopted in the present invention includes the following steps

(1) Prepare a mixed solution of Pt precursor and non-precious metal precursor with deionized water, and the atomic ratio of Pt to non-precious metal is 1:30-30:1, preferably 1:10-10:1. Stir to mix well.

(2) In high-viscosity alcohol, add a carrier, and ultrasonicate vigorously for 30-60min to make it evenly dispersed;

(3) The dispersion is stirred at room temperature for _30-60min , and N or Ar is introduced into the stirring process to form an inert atmosphere of the reaction system;

(4) adding a reducing agent to the above-mentioned dispersion, then adding the mixed solution of Pt and non-precious metal precursors formed in step (1), so that the total molar concentration of Pt and non-precious metal elements in the system is 0.1-20 mmol/L (preferably 0.5-10 mmol/L), the molar concentration of the reducing agent is 1-100 times (preferably 5-30 times) the total molar concentration of Pt and non-noble metal elements. The reaction is carried out at a reaction temperature of 0-160°C (preferably 25-90°C) for 0.5-24h (preferably 3-16h).

5) Centrifugal washing, washing with a mixture of ethanol and deionized water and adding an appropriate amount of dilute nitric acid to remove unstable non-precious metals and form a Pt-rich surface layer; Pt-based alloy catalyst product;

The non-precious metals are Fe, Co, Ni, Cu, Mn, Mo, Cr.

Described Pt precursor is Pt nitrate, amine complex, hydrohalic acid or hydrohalic acid salt; Described non-precious precursor is corresponding metal nitrate, sulfate, halide, amine complex , hydrohalic acid or hydrohalide salt; the high-viscosity alcohol is ethylene glycol, polyethylene glycol, glycerol, etc., and the high-viscosity alcohol doubles as a solvent and a protective agent; the carrier is conductive carbon black, carbon nanomaterials Carbon supports such as tubes, graphene, and carbon nanocages, conductive polymers such as polyaniline, polypyrrole, and polydopamine, oxides such as TiO ₂ , SnO ₂ , WO ₃ , metal carbides, metal nitrides, and two or more of the above complex formed.

Based on the above technical solutions, preferably, the reducing agent is hydrazine hydrate, tetrabutyl borohydride, citric acid, sodium citrate, and ascorbic acid.

Based on the above technical solutions, preferably, the stirring reaction temperature in step 4) is 25-90°C.

Based on the above technical solution, preferably, the stirring reaction time in step 4) is 3-16h.

Based on the above technical solution, preferably, in step 5), the total molar concentration of Pt and non-precious metal elements is 0.5-10 mmol/L.

Another aspect of the present invention provides a catalyst prepared by the above method, the catalyst is a supported core-shell structure, and the supported material is a core-shell structure; the core of the core-shell structure is an alloy of Pt and a non-precious metal; the core The shell of the shell structure is Pt; the shape of the core-shell structure is spherical nanoparticles with a particle size of 1-3 nm.

Based on the above technical solutions, preferably, in the catalyst, the atomic ratio of Pt to non-precious metal is >10.

Based on the above technical solutions, preferably, the catalyst has a Pt-rich surface layer, and the number of layers is 2-5.

Another aspect of the present invention provides an application of the above catalyst in a low temperature fuel cell.

beneficial effect

(1) The preparation method is simple in process, low in energy consumption, and environmentally friendly, which is conducive to realizing large-scale production;

(2) No surfactant is used, the catalyst particle size is small, the particle size is uniform, the distribution on the carrier is uniform, and the effective active area is significantly higher than that of commercial Pt/C;

(3) The catalyst only contains a trace amount of transition metals, which greatly reduces the performance degradation caused by the dissolution of transition metals during battery operation;

(4) The catalyst has a Pt shell structure, which can effectively avoid the dissolution of transition metals and further improve the stability of the catalyst;

(5) The catalyst exhibits significantly better activity and stability than commercial Pt/C in both electrochemical and practical fuel cell tests.

Description of drawings

FIG. 1 is a TEM image of the Pt ₃₆ Co/C catalyst prepared in Example 1 of the present invention.

2 is an EDS linear scan diagram of the Pt ₃₆ Co/C catalyst prepared in Example 1 of the present invention.

FIG. 3 is a performance comparison diagram of the Pt ₃₆ Co/C catalyst prepared in Example 1 of the present invention and the 20% Pt/C (JM) catalyst half-cell before and after 1500 cycles of accelerated decay.

Figure 4 is a comparison diagram of the performance (IV curve) of the Pt ₃₆ Co/C catalyst (4a) prepared in Example 1 of the present invention and the 20% Pt/C (JM) catalyst (4b) full cell before and after the accelerated decay of 3000 cycles.

5 is a TEM image of the Pt ₂₂ Ni alloy nanocatalyst prepared in Example 2 of the present invention.

6 is a cyclic voltammetry (CV) curve diagram of the Pt ₂₂ Ni/C alloy catalyst prepared in Example 2 of the present invention and the 20% Pt/C (JM) catalyst of Johnson Matthey Company.

7 is a graph of oxygen reduction polarization (ORR) curves of the Pt ₂₂ Ni/C alloy catalyst prepared in Example 2 of the present invention and the 20% Pt/C (JM) catalyst of Johnson Matthey Company.

8 is a TEM image of the Pt ₃₀ Cu/C alloy catalyst prepared in Example 3 of the present invention.

9 is a TEM image of the Pt ₈₈ Fe/C alloy catalyst prepared in Example 4 of the present invention.

Detailed ways

Example 1

(1) Dissolve H ₂ PtCl ₆ ·6H ₂ O and CoCl ₂ ·6H ₂ O in 2 ml of deionized water, and the atomic ratio of Pt to Co is 1:2. Stir to mix well.

(2) In ethylene glycol, add carbon black XC-72, and ultrasonically disperse evenly.

(3) The dispersion was stirred at room temperature for 30min, and N ₂ was introduced into the stirring process to form an inert atmosphere of the reaction system;

(4) adding the reducing agent hydrazine hydrate into the above-mentioned dispersion, then adding the mixed solution of Pt and Co precursors, so that the total concentration of Pt and Co elements in the system is 3mmol/L, and the molar concentration of the reducing agent is the total concentration of Pt and Ni elements. 10 times the molar concentration. Stir at room temperature for 6 h.

(5) 2 mol/L dilute nitric acid was added to the mixed solution of ethanol and deionized water, so that the pH of the mixed solution was ≈ 2, and the catalyst was washed with it.

(6) The catalyst was vacuum-dried at 80 °C for 10 h to obtain a Pt ₃₆ Co/C catalyst. The actual atomic ratio of Pt to Co was 36:1.

FIG. 1 is a TEM image of the Pt-Co alloy nanoparticles of this embodiment, which shows that Pt-Co has a smaller particle size and a uniform distribution on the carbon support.

FIG. 2 is an EDS linear scan diagram of the Pt-Co alloy nanoparticles prepared in the present embodiment, which reveals the existence of trace Co elements and Pt shell structure in the Pt-Co alloy.

FIG. 3 is a performance comparison diagram of the Pt ₃₆ Co/C catalyst prepared in the embodiment of the present invention and the 20% Pt/C (JM) catalyst half-cell before and after 1500 cycles of accelerated decay. Scan speed 50mV s ^-1 , test at 25℃. It can be seen from the figure that the half-cell performance and stability of the Pt ₃₆ Co/C catalyst are higher than those of commercial Pt/C.

FIG. 4 is a comparison diagram of the performance (IV curve) of the Pt ₃₆ Co/C catalyst prepared in this example and the 20% Pt/C (JM) catalyst before and after 3000 cycles of accelerated decay. Scan speed 100mV s ^-1 , test at 65℃. It can be seen from the figure that the full cell performance and stability of the Pt ₃₆ Co/C catalyst are higher than those of commercial Pt/C.

Example 2

(1) H ₂ PtCl ₆ ·6H ₂ O and NiCl ₂ ·6H ₂ O were dissolved in 2 ml of deionized water, and the atomic ratio of Pt to Ni was 3:1. Stir to mix well.

(2) In ethylene glycol, carbon black XC-72 is added, and ultrasonic dispersion is mixed;

(3) The dispersion was stirred at room temperature for 40min, and N ₂ was introduced into the stirring process to form an inert atmosphere of the reaction system;

(4) adding the reducing agent sodium borohydride into the above-mentioned dispersion liquid, then adding the mixed solution of Pt and Ni precursors, so that the total molar concentration of Pt and Ni elements in the system is 3.6 mmol/L, and the molar concentration of the reducing agent is Pt and Ni. 18.5 times the total molar concentration of Ni elements. Stir at room temperature for 3 h.

(5) 2 mol/L dilute nitric acid was added to the mixed solution of ethanol and deionized water, so that the pH of the mixed solution was ≈ 3, and the catalyst was washed with it.

(6) The catalyst was vacuum-dried at 60° C. for 12 h to obtain the product.

FIG. 5 is a TEM image of the Pt ₂₂ Ni alloy nanoparticles prepared in this example. The average particle diameter of the particles was 1.5 nm.

FIG. 6 is a cyclic voltammetry (CV) curve diagram of the Pt ₂₂ Ni/C alloy catalyst prepared in this example and the 20% Pt/C (JM) catalyst of Johnson Matthey Company. The solution was 0.1M HClO ₄ saturated with N ₂ , the scanning speed was 50mVs ^-1 , and the test was performed at room temperature. Compared with Pt/C(JM), the reduction peak potential of Pt alloy surface oxide shifted positively, indicating that the surface oxide of Pt alloy was more easily removed, which accelerated the reaction rate of ORR.

FIG. 7 is a graph of oxygen reduction polarization (ORR) curves of the Pt ₂₂ Ni/C alloy catalyst prepared in this example and the 20% Pt/C (JM) catalyst of Johnson Matthey Company. The solution is 0.1M HClO ₄ saturated with O ₂ , the scanning speed is 10mVs ^-1 , the forward scanning is performed, the RDE speed is 1600 rpm, and the test is carried out at room temperature. It can be seen from the oxygen reduction curve that the half-wave potential of Pt-Ni/C alloy is higher than that of Pt/C(JM).

Example 3

(1) Dissolve H ₂ PtCl ₆ ·6H ₂ O and Cu(NO ₃ ) ₂ in 2 ml of deionized water, and the atomic ratio of Pt to Cu is 1:3. Stir to mix well.

(2) In ethylene glycol, add carbon black XC-72, and ultrasonically disperse evenly.

(3) The dispersion was stirred at room temperature for 30 min, and Ar was introduced into the stirring process to form an inert atmosphere of the reaction system.

(4) adding the reducing agent ascorbic acid to the above-mentioned dispersion liquid, then adding the mixed solution of Pt and Cu precursors, so that the total concentration of Pt and Cu elements in the system is 5mmol/L, and the molar concentration of the reducing agent is the total moles of Pt and Cu elements 15 times the concentration. Stir at 80°C reaction temperature for 3h.

(5) 2 mol/L dilute nitric acid was added to the mixed solution of ethanol and deionized water, so that the pH of the mixed solution was ≈ 2, and the catalyst was washed with it.

(6) The catalyst was vacuum-dried at 40° C. for 24 hours to obtain the product.

FIG. 8 is a TEM photograph of the Pt ₃₀ Cu alloy nanoparticles prepared in this example. The average particle size of the particles is 1.6nm

Example 4

(1) H ₂ PtCl ₆ ·6H ₂ O and FeCl ₃ ·6H ₂ O were dissolved in 2 ml of deionized water, and the atomic ratio of Pt to Fe was 1:10. Stir to mix well.

(2) In polyethylene glycol, carbon nanotubes are added, and ultrasonic dispersion is uniform.

(3) The dispersion was stirred at room temperature for 60 min, and Ar was introduced into the stirring process to form an inert atmosphere of the reaction system.

(4) adding reducing agent ascorbic acid to above-mentioned dispersion liquid, then adding Pt and Fe precursor mixed solution, so that the total concentration of Pt and Fe elements in the system is 10mmol/L, and the molar concentration of reducing agent is the total moles of Pt and Fe elements 20 times the concentration. Stir at a reaction temperature of 140 °C for 12 h.

(5) 2 mol/L dilute nitric acid was added to the mixed solution of ethanol and deionized water, so that the pH of the mixed solution was ≈ 2, and the catalyst was washed with it.

(6) The catalyst was vacuum-dried at 100° C. for 8 h to obtain the product.

FIG. 9 is a TEM photograph of the Pt ₈₈ Fe alloy nanoparticles prepared in this example. The average particle diameter of the particles was 1.7 nm.

Example 5

(1) KPtCl ₄ , Ni(NO ₃ ) ₂ and Mo(NO ₃ ) ₂ were dissolved in 2 ml of deionized water, and the atomic ratio of Pt to Ni and Mo was 5:1:1. Stir to mix well.

(2) In glycerol, add carbon nanotubes, and ultrasonically disperse uniformly.

(3) The dispersion was stirred at room temperature for 60 min, and N ₂ was introduced into the stirring process to form an inert atmosphere of the reaction system.

(4) adding the reducing agent citric acid to the above-mentioned dispersion, then adding the mixed solution of Pt and Mo precursors, so that the total concentration of Pt, Ni, and Mo elements in the system is 1 mmol/L, and the molar concentration of the reducing agent is Pt, Ni , 10 times the total molar concentration of Mo elements. Stir at 120°C reaction temperature for 8h.

(5) 2 mol/L dilute nitric acid was added to the mixed solution of ethanol and deionized water, so that the pH of the mixed solution was ≈ 3, and the catalyst was washed with it.

(6) The catalyst was vacuum-dried at 70° C. for 24 h to obtain the product.

Claims (10)

1. A preparation method of a non-noble metal modified platinum-based catalyst is characterized by comprising the following steps,

1) preparing a mixed solution of a Pt precursor and a non-noble metal precursor by using deionized water, and uniformly stirring; in the mixed solution, the atomic ratio of Pt to non-noble metal is 1:30-30: 1;

2) adding a carrier into high-viscosity alcohol, and performing ultrasonic dispersion to obtain a dispersion liquid;

3) the dispersion was stirred at room temperature and N was added₂Or Ar is over 30min to form inert dispersion liquid;

4) adding a reducing agent into the inert dispersion liquid, then adding the mixed solution obtained in the step (1) to form a reaction system, and then reacting at 0-160 ℃ for 0.5-24 h; the total molar concentration of Pt and non-noble metal elements in the reaction system is 0.1-20mmol/L, and the molar concentration of the reducing agent is 1-100 times of the total molar concentration of the Pt and non-noble metal elements;

5) centrifugally washing, namely washing by using a mixture of ethanol and deionized water and adding a proper amount of dilute nitric acid, and then drying in vacuum at 40-100 ℃ for 6-24h to obtain the catalyst; the non-noble metal is Fe, Co, Ni, Cu, Mn, Mo, Cr.

2. The production method according to claim 1, wherein the Pt precursor is a nitrate, an amine complex, a hydrohalic acid, or a hydrohalic acid salt of Pt; the non-noble metal precursor is nitrate, sulfate, halide, amine complex, halogen acid or halogen acid salt of corresponding metal; the high viscosity alcohol is ethylene glycol, polyethylene glycol and glycerol; the carrier is conductive carbon black, carbon nano tubes, graphene, carbon nano, polyaniline, polypyrrole, polydopamine, TiO₂、SnO₂、WO₃At least one of metal carbide and metal nitride.

3. The method of claim 1, wherein the reducing agent is hydrazine hydrate, tetrabutyl borohydride, citric acid, sodium citrate, ascorbic acid.

4. The process according to claim 1, wherein the reaction temperature in the step 4) is 25 to 90 ℃ with stirring.

5. The process according to claim 1 or 4, wherein the reaction time in step 4) is 3 to 16 hours with stirring.

6. The process according to claim 1, wherein in step 5), the total molar concentration of Pt and non-noble metal elements is 0.5-10 mmol/L.

7. A catalyst prepared by the process of claim 1, wherein: the catalyst is in a supported core-shell structure, and the supported object is in a core-shell structure; the core of the core-shell structure is an alloy of Pt and non-noble metal; the shell of the core-shell structure is Pt; the shape of the core-shell structure is spherical nano particles with the particle size of 1-3 nm.

8. The catalyst of claim 7, wherein: in the catalyst, the atomic ratio of Pt to non-noble metal is more than 10.

9. The catalyst of claim 7, wherein: the catalyst has a shell of 2-5 layers.

10. Use of the catalyst of claim 7 in a low temperature fuel cell.

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