CN108736031A - A kind of self-supporting PtCo alloy nanoparticle catalyst and the preparation method and application thereof - Google Patents

Abstract

The invention relates to a self-supporting PtCo alloy nanoparticle catalyst and its preparation method and application. The specific method is to synthesize a three-dimensional self-supporting cobalt-based metal-organic framework (Co-MOFs) nanorod array structure on a carbon cloth by means of a liquid phase. A three-dimensional porous nitrogen-doped carbon-coated metal cobalt nanoparticle (Co@N‑C) nanorod structure was obtained by high-temperature carbothermal reduction technology, and this was used as a template to utilize the difference in the redox potential of metal Pt and Co by simple Nitrogen-doped carbon/PtCo (PtCo@N‑C) porous catalyst was finally obtained by the electroporation reaction method. Compared with the prior art, the composite catalyst of the present invention does not require binders and conductive additives, and has excellent methanol oxidation performance and CO toxicity resistance. The flexible carbon cloth substrate is used as a current collector, which is bendable and foldable, and has very good mechanical properties .

Description

A kind of self-supporting PtCo alloy nanoparticle catalyst and its preparation method and application

technical field

The invention relates to the technical field of fuel cells, in particular to a self-supporting PtCo alloy nanoparticle catalyst and a preparation method and application thereof.

Background technique

As a high-efficiency energy conversion device, fuel cells have the potential of low cost and zero emission, and are considered to be an important way to solve human's growing energy crisis and environmental pollution problems. However, methanol has the advantages of high commercialization, high specific energy, and good portability. Therefore, direct methanol fuel cells have very promising application prospects and have attracted widespread attention. Among many electrocatalysts, platinum and platinum-based alloys are still the most effective and stable catalysts in methanol oxidation. However, the limited reserves and high price of platinum greatly limit its large-scale commercial application. In addition, the catalytic performance of platinum is also limited by its slow methanol oxidation kinetics and CO poisoning.

Contents of the invention

The purpose of the present invention is to provide a self-supporting PtCo alloy nanoparticle catalyst with good catalytic activity, strong anti-toxicity and good mechanical properties and its preparation method and application in order to overcome the above-mentioned defects in the prior art.

The purpose of the present invention can be achieved through the following technical solutions: a self-supporting PtCo alloy nanoparticle catalyst, the catalyst includes three-dimensional porous nitrogen-doped carbon and Pt and Co coated inside the three-dimensional porous nitrogen-doped carbon, wherein, the The mass ratio of Pt and Co is (0.5-0.6): 1. The total mass of Pt and Co accounts for 43%-48% of the mass of the catalyst, and the three-dimensional porous nitrogen-doped carbon has an array structure. The invention adopts Pt and Co together as active components of the catalyst, the combination of Pt and Co reduces the electron binding energy in the Pt, promotes the C-H cracking reaction at low potential, thereby improving the activity and toxicity resistance of the catalyst. At the same time, since the cobalt-based metal organic framework material precursor has a three-dimensional array structure, the porous nitrogen-doped carbon after calcination is also an array structure. The highly graphitized porous nitrogen-doped carbon nanorod array has a large specific surface area and high electrical conductivity, which provides an ideal support for the dispersion of PtCO nanoparticles and facilitates the migration of ions/protons; the doped nitrogen element can strengthen the alloy particles The interaction with carbon improves the stability of the catalyst; and the intrinsic catalytic ability of porous nitrogen-doped carbon also makes a certain contribution to the improved catalytic activity.

A method for preparing the self-supporting PtCo alloy nanoparticle catalyst as described above, comprising the following steps:

(1) Put the carbon cloth into an aqueous solution of acetone for ultrasonic treatment, wash and dry, and then place it in a precursor solution to form a cobalt-based metal organic framework, wherein the precursor solution is cobalt nitrate and dimethylimidazole mixed aqueous solution;

(2) calcining the cobalt-based metal-organic framework to obtain a three-dimensional porous nitrogen-doped carbon coated with Co nanoparticles;

(3) Soak the obtained three-dimensional porous nitrogen-doped carbon coated with Co nanoparticles in H ₂ PtCl ₄ Pt solution to obtain the self-supporting PtCo alloy nanoparticle catalyst.

Since the carbon cloth made of carbon fiber is a good three-dimensional conductive substrate material, its function can increase the conductivity specific surface area of the prepared material on the one hand, which is beneficial to increase the active sites; on the other hand, it grows on the carbon cloth. The active material can be directly used as a catalytic electrode, eliminating the need to make electrodes like other powder catalysts. During the whole preparation process, Co is gradually replaced by Pt from outside to inside to form alloy particles.

The carbon cloth is ultrasonically treated in an aqueous solution of acetone for 20 to 30 minutes, and the ultrasonic wave is used to clean the carbon cloth.

The washing uses deionized water, and the drying temperature is 60-80°C.

In the precursor solution, the molar ratio of cobalt nitrate and dimethylimidazole is 1:(15-20).

The calcination is carried out in a mixed atmosphere of Ar and H ₂ , wherein Ar accounts for 90% to 95% of the total volume of Ar and H ₂ . The addition of H ₂ can promote the catalytic effect of Co during the calcination process, and some carbon nanotubes grow on the surface of the array structure, which increases the specific surface area of the structure.

Raise the temperature to 700-900°C at less than 5°C/min, keep it warm for 2-4 hours, and then cool down to room temperature naturally. 700-900°C can make the cobalt-based metal-organic framework array highly graphitized and increase the conductivity.

The concentration of the H ₂ PtCl ₄ Pt solution is 0.5-2 mmol/L, and the soaking time of the three-dimensional porous nitrogen-doped carbon coated with Co nanoparticles in the H ₂ PtCl ₄ Pt solution is 2-4 minutes.

An application of the self-supporting PtCo alloy nanoparticle catalyst as described above, the catalyst is used in the anode of methanol fuel cell. Methanol oxidation reaction occurs at the anode of the methanol fuel cell, and oxygen reduction reaction occurs at the cathode. The material prepared by the invention is a methanol oxidation catalyst, so it is used for the anode of the methanol fuel cell.

Compared with the prior art, the beneficial effects of the present invention are reflected in the following aspects:

(1) When the catalyst is used in the anode of a methanol fuel cell, the methanol oxidation initial potential is high and the anode current density is large;

(2) When the catalyst is used in the anode of a methanol fuel cell, it has excellent CO toxicity resistance and durability.

Description of drawings

Figure 1 is a three-dimensional porous Co@N-C scanning electron microscope image;

Figure 2 is a three-dimensional PtCo@N-C catalyst plane scanning electron microscope picture;

Figure 3 shows the CV curves of PtCo@NC and Pt/C tested at a sweep rate of 50mV/s in 0.5MH ₂ SO ₄ electrolyte.

Figure 4 shows the CV curves of PtCo@NC and Pt/C tested at a scan rate of 50mV/s in the electrolyte of 0.5M CH ₃ OH+0.5MH ₂ SO ₄ .

Figure 5 is a comparison of the peak current densities of PtCo@NC and Pt/C in the electrolyte of 0.5M CH ₃ OH+0.5M H ₂ SO ₄ with increasing cycle times.

Figure 6 shows the CO anti-toxicity CV curves of PtCo@NC and Pt/C tested in 0.5MH ₂ SO ₄ electrolyte.

Detailed ways

The embodiments of the present invention are described in detail below. This embodiment is implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operating procedures are provided, but the protection scope of the present invention is not limited to the following implementation example.

Example 1

A preparation method of a self-supporting PtCo alloy nanoparticle catalyst, comprising the following steps:

Fabrication of Co-MOFs Nanorod Arrays on Carbon Cloth

First choose carbon cloth as the base, model: WOS1002. The carbon cloth was put into acetone and deionized water for ultrasonic treatment for 20 minutes, and finally rinsed with deionized water and put into a blast drying oven for drying.

Prepare the Co-MOFs precursor solution: quickly add 40ml 25mM cobalt nitrate (Co(NO ₃ ) ₂ 6H ₂ O) to 40ml 0.4M dimethylimidazole (C ₄ H ₆ N ₂ ) aqueous solution, then stir .

At 30° C., soak the treated carbon cloth in the Co-MOFs precursor solution for 4 hours to react. Then rinse with deionized water.

Repeat the above steps to grow Co-MOFs for the second time under the same temperature and reaction time.

Fabrication of Co@N-C Nanorod Arrays on Carbon Cloth

The Co-MOFs nanorod array prepared on the carbon cloth was annealed at 800°C in an Ar/H ₂ (5%H ₂ , 95%Ar) environment for 2 hours, wherein the heating rate was 5°C/ minute. The Co@NC nanorod array structure was obtained after natural cooling (Fig. 1).

Fabrication of PtCo@N-C Nanorod Arrays on Carbon Cloth

The prepared PtCo@NC nanorod array on the carbon cloth was soaked in a stirring 1 mM chloroplatinic acid (H ₂ PtCl ₆ ·6H ₂ O) solution for 3 minutes, which was marked as PtCo@NC. The reaction equation is:

Co+PtCl ₄ ^2- →Co ²⁺ +Pt+ ^4Cl-

The PtCo@NC nanorod array prepared on the carbon cloth was annealed at 400°C in an Ar/H ₂ (5%H ₂ , 95%Ar) environment for 1 hour, wherein the heating rate was 3.5°C/ minute. After natural cooling, the PtCo@NC nanorod array structure was obtained (Fig. 2).

The masses of Pt and Co in the prepared PtCo@NC are 0.278 mg cm ^-2 and 0.533 mg cm ^-2 , and the corresponding atomic number ratio is 14:86.

The present invention synthesizes a three-dimensional Co-MOFs nanorod structure with a large specific surface area by means of liquid phase, and obtains a Co@N-C structure after annealing treatment, which is used as a carrier, and a series of Pt loads are prepared by using a simple Pt precursor soaking method The PtCo@N-C catalyst, and the electrocatalytic performance of the catalyst was systematically tested and analyzed.

The electrocatalytic performance of the prepared PtCo@N-C catalyst was tested by an electrochemical workstation under a three-electrode system. Among them, the PtCo@N-C catalyst was used as the working electrode, the Ag/AgCl (+0.197 V vs RHE) soaked in saturated KCl solution was used as the reference electrode, and the graphite rod was used as the counter electrode.

Before the measurement, high-purity Ar was bubbled into the electrolyte for 20 min to remove CO and O ₂ in the solution.

The electrochemically active area of the prepared PtCo@NC catalyst is obtained by testing the voltammetric curve (CV) in a solution of 0.5MH ₂ SO ₄ , wherein the test voltage range is 0 to 1.0V vs RHE, and the sweep rate is 50mV s ^-1 .

The electrochemically active areas of the prepared PtCo@NC and Pt/C catalysts were 20m ² /g and 14.2m ² /g, respectively, and the PtCo@NC catalyst exhibited a larger electrochemically active area ( FIG. 3 ).

The methanol oxidation performance of the prepared PtCo@NC catalyst is obtained by testing the voltammetry curve (CV) in a mixed solution containing 0.5MH ₂ SO ₄ and 0.5MCH ₃ OH, wherein the test voltage range is 0-1.2V vs. RHE, the scan rate is 50mV s ^-1 .

The prepared PtCo@NC has a more negative initial voltage (0.563V<0.642V) and a larger positive sweep current density (433.5mA mg ^-1 >140mA mg ^-1 ) than the Pt/C catalyst. Therefore, the PtCo@NC catalyst exhibits better methanol oxidation activity (Fig. 4).

The methanol oxidation stability of the prepared PtCo@NC catalyst is obtained by testing the CV curve of 100 consecutive cycles in a mixed solution of 0.5MH ₂ SO ₄ and 0.5M CH ₃ OH, wherein the test voltage range is 0- 1.2Vvs.RHE, sweep rate is 50mV s ^-1 .

The anodic peak current density retention rates of the prepared PtCo@N-C and Pt/C catalysts after 100 cycles were 94.4% and 68.7% of the peak values, respectively, indicating that the durability of the PtCo@N-C catalysts is due to the commercial Pt/C (Fig. 5 ).

The CO anti-poison performance of the prepared PtCo@NC catalyst is obtained by testing the CV curve in a CO-saturated 0.5MH ₂ SO ₄ solution, wherein the test voltage range is -0.1 to 1.4V vs RHE, and the sweep rate is 50mV s ^-1 . Before the measurement, high-purity CO gas and Ar gas were passed into the electrolyte for 15 minutes each to ensure that the active sites of the catalyst were covered with enough CO and there was no CO in the solution.

The CO desorption peaks of the prepared PtCo@N-C and Pt/C catalysts are at 0.92 V and 1.03 V, respectively, and the more negative CO desorption peak of PtCo@N-C proves that it has more excellent CO solubility (Figure 6).

Therefore, the PtCo@N-C catalyst prepared in this example has excellent methanol oxidation current density, CO toxicity resistance and durability.

Example 2

Adopt the preparation method similar to embodiment 1, difference is:

(1) The carbon cloth is ultrasonically treated in an aqueous solution of acetone for 20 minutes, and the drying temperature of the carbon cloth is 60°C;

(2) The molar ratio of cobalt nitrate and dimethylimidazole in the precursor solution is 1:15.

(3) The calcination is carried out in a mixed atmosphere of Ar and H ₂ , wherein Ar accounts for 90% of the total gas volume; the calcination temperature is 700°C, and the calcination time is 4h;

(4) The concentration of the H ₂ PtCl ₄ Pt solution used for soaking is 0.5mmol/L, and the soaking time is 4min.

The catalyst prepared in this example is used in the anode of the methanol fuel cell, and it is found through testing that it has a large current density and has good CO poisoning performance.

Example 3

Adopt the preparation method similar to embodiment 1, difference is:

(1) The carbon cloth is ultrasonically treated in an aqueous solution of acetone for 30 minutes, and the drying temperature of the carbon cloth is 80°C;

(2) The molar ratio of cobalt nitrate and dimethylimidazole in the precursor solution is 1:-20.

(3) The calcination is carried out in a mixed atmosphere of Ar and H ₂ , wherein Ar accounts for 90% to 95% of the total gas volume; the calcination temperature is 900°C, and the calcination time is 2h;

(4) The concentration of the H ₂ PtCl ₄ Pt solution used for soaking is 2mmol/L, and the soaking time is 2min.

The catalyst prepared in this example is used in the anode of the methanol fuel cell, and it is found through testing that it has a large current density and has good CO poisoning performance.

Claims (9)

1. A self-supporting PtCo alloy nanoparticle catalyst, characterized in that the catalyst includes three-dimensional porous nitrogen-doped carbon and Pt and Co coated inside the three-dimensional porous nitrogen-doped carbon, wherein the mass of the Pt and Co The ratio is (0.5-0.6): 1. The total mass of Pt and Co accounts for 43%-48% of the mass of the catalyst, and the three-dimensional porous nitrogen-doped carbon has an array structure. 2. a preparation method of self-supporting PtCo alloy nanoparticle catalyst as claimed in claim 1, is characterized in that, comprises the following steps: (1) Put the carbon cloth into an aqueous solution of acetone for ultrasonic treatment, wash and dry, and then place it in a precursor solution to form a cobalt-based metal organic framework, wherein the precursor solution is cobalt nitrate and dimethylimidazole mixed aqueous solution; (2) calcining the cobalt-based metal-organic framework to obtain a three-dimensional porous nitrogen-doped carbon coated with Co nanoparticles; (3) Soak the obtained three-dimensional porous nitrogen-doped carbon coated with Co nanoparticles in H ₂ PtCl ₄ Pt solution to obtain the self-supporting PtCo alloy nanoparticle catalyst. 3 . The method for preparing a self-supporting PtCo alloy nanoparticle catalyst according to claim 2 , wherein the carbon cloth is ultrasonically treated in an aqueous solution of acetone for 20 to 30 minutes. 4 . 4 . The method for preparing a self-supporting PtCo alloy nanoparticle catalyst according to claim 2 , wherein deionized water is used for the washing, and the drying temperature is 60-80° C. 5. the preparation method of a kind of self-supporting PtCo alloy nanoparticle catalyst according to claim 2, is characterized in that, in described precursor solution, the mole of cobalt nitrate and dimethylimidazole is 1:(15～20) . 6. the preparation method of a kind of self-supporting PtCo alloy nanoparticle catalyst according to claim _{2, is characterized in that, described calcining is carried out in the mixed atmosphere of Ar and H , wherein, Ar accounts for Ar and H 2 total} volume 90% to 95% of that. 7. The preparation method of a self-supporting PtCo alloy nanoparticle catalyst according to claim 6, characterized in that the calcination step is: heating up to 700-900°C at a rate of less than 5°C/min, and keeping the temperature for 2-4h After that, let it cool down to room temperature naturally. 8. The method for preparing a self-supporting PtCo alloy nanoparticle catalyst according to claim 2, wherein the concentration of the H ₂ PtCl ₄ Pt solution is 0.5 to 2 mmol/L, and the three-dimensional coating of Co nanoparticles The soaking time of the porous nitrogen-doped carbon in the H ₂ PtCl ₄ Pt solution is 2-4 minutes. 9. The application of a self-supporting PtCo alloy nanoparticle catalyst as claimed in claim 1, characterized in that the catalyst is used for the anode of a methanol fuel cell.