CN113903928A

CN113903928A - Preparation method and application of Sb/NC electrocatalyst

Info

Publication number: CN113903928A
Application number: CN202111021849.3A
Authority: CN
Inventors: 孙盼盼; 龚涛; 谢幸; 孙小华; 黄妞
Original assignee: China Three Gorges University CTGU
Current assignee: China Three Gorges University CTGU
Priority date: 2021-09-01
Filing date: 2021-09-01
Publication date: 2022-01-07
Anticipated expiration: 2041-09-01
Also published as: CN113903928B

Abstract

The invention provides a preparation method and application of an Sb/NC electrocatalyst. Adding SbCl into ZIF-8 precursor₃Soaking and stirring the obtained ethanol solution, then centrifugally washing the obtained product by using ethanol, drying the product in a vacuum drying oven, uniformly grinding the obtained powder, placing the powder in a tubular furnace, and carrying out high-temperature pyrolysis in an inert atmosphere to obtain the novel Sb/NC electrocatalyst. The novel electrocatalyst has the advantages of simple preparation process, large specific surface area, excellent electrocatalytic oxygen reduction activity, good stability and the like, and has potential application in the field of oxygen reduction.

Description

Preparation method and application of Sb/NC electrocatalyst

Technical Field

The invention relates to a high-efficiency and low-cost oxygen reduction electrocatalyst, in particular to a preparation method and oxygen reduction performance of an Sb/NC electrocatalyst, and belongs to the field of oxygen reduction application.

Background

The slow kinetics of the cathodic electrochemical Oxygen Reduction Reaction (ORR) and the excessively high potential limit the overall performance of high efficiency fuel cells and metal air cells. Practice has shown that precious metal Pt-based materials are the most efficient ORR electrocatalysts, but their high cost, scarcity, and methanol tolerance have prompted the search for highly efficient and durable non-precious metal catalysts. Among the many exploratory directions, nitrogen-doped carbon-supported transition metal (M/NC) materials obtained by pyrolysis processes are considered the most promisingCan replace non-noble metal ORR catalyst of noble metal Pt. And pyrolyzing Metal Organic Frameworks (MOFs) is an effective way to develop high-activity M/NC catalysts. Taking ZIF-8 as an example, by adjusting and controlling synthesis conditions (metal ion type, content, pyrolysis temperature, pyrolysis atmosphere, etc.), a high-activity M/NC catalyst can be obtained. Furthermore, Zn in ZIF-8 during pyrolysis at high temperature²⁺Is reduced into Zn atoms and then volatilized, and simultaneously generates a large number of micro/mesopores in the NC matrix, thereby increasing the porosity and specific surface area of the product. These characteristics are important for improving the utilization efficiency of catalytic active sites, enhancing the mass transfer rate of reaction substrates and catalytic products on the electrode interface and finally improving the ORR performance of the material. However, to achieve further improvements in M/NC catalyst activity, more efficient regulation strategies are also needed.

Antimony (Sb) is a main group element in the periodic Table of elements, and has a melting point of 630 ℃. If Sb salts are introduced into the M/NC precursor, Sb is formed during pyrolysis at high temperature³⁺It is also reduced to Sb atoms and volatilized, further creating a pore structure in the NC matrix. Based on the method, the Sb salt is adsorbed on the surface of the ZIF-8 serving as a precursor, and then the ZIF-8 pore structure is further modified through high-temperature pyrolysis, so that the Sb/NC electrocatalyst is successfully prepared. The novel electrocatalyst has the advantages of simple preparation process, large specific surface area, excellent electrocatalytic oxygen reduction activity, good stability and the like, and has potential application in the field of oxygen reduction.

Disclosure of Invention

The invention aims to provide an Sb/NC electrocatalyst with excellent oxygen reduction performance. The preparation method comprises the following specific steps:

step 1: adding Zn (NO)₃)₂ ·6H₂Dissolving O in N, N-dimethylformamide and a mixed solvent of ethanol and methanol to obtain a solution A; dissolving 2-methylimidazole in a mixed solvent of N, N-dimethylformamide and methanol to obtain a solution B. Mixing the solution A and the solution B, stirring at room temperature, then centrifugally washing the obtained product with methanol, and finally drying in a vacuum drying oven to obtain a ZIF-8 precursor;

step 2:preparation of a composition containing SbCl₃Adding a ZIF-8 precursor into the ethanol solution, soaking and stirring, then centrifugally washing with ethanol, and drying in a vacuum drying oven;

and step 3: and uniformly grinding the obtained powder, placing the powder in the center of a tube furnace, and carrying out high-temperature pyrolysis in an inert atmosphere to obtain the Sb/NC electrocatalyst.

The molar concentration of Zn (NO3) 2.6H 2O is 0.1-0.5 mmol/mL.

The volume ratio of the N, N-dimethylformamide to the ethanol to the methanol is 3: 0.8-1.2: 0.8-1.2.

The concentration of the 2-methylimidazole is 1-3 mmol/mL.

The volume ratio of the N, N-dimethylformamide to the methanol is 3: 1-2.

The concentration of the ethanol solution of SbCl3 is 7-9 mM, and the soaking and stirring time is 1-3 h.

The inert atmosphere comprises Ar gas or nitrogen, and the annealing is carried out for 1-3h by heating to 800-900 ℃ in a tube furnace at the heating rate of 5-6 ℃/min.

The invention also provides an application of the prepared Sb/NC electrocatalyst as an oxygen reduction reaction catalyst.

The Sb/NC electrocatalyst and the preparation method have the following remarkable characteristics:

(1) the prepared catalyst has high porosity and large specific surface area, and is favorable for the transmission of reaction substrates and catalytic products on an electrode interface in the oxygen reduction process.

(2) The Sb/NC electrocatalyst has the advantages of excellent electrocatalytic oxygen reduction activity, good stability and the like, and has potential application in the field of oxygen reduction.

Drawings

Figure 1 XRD patterns of samples prepared in examples 1, 2, 3.

FIG. 2 TEM images of samples prepared in examples 1 and 2.

FIG. 3N of sample prepared in example 2₂Adsorption-desorption curve diagram and pore size distribution curve diagram.

FIG. 4 LSV profiles of samples prepared according to examples 1, 2 and 3.

FIG.

5Examples

1, 2, 3 the oxygen reduction electron transfer numbers (n) and H of the prepared samples₂O₂The yield chart.

FIG. 6 stability plots of the samples prepared in example 2 and commercial Pt/C.

Detailed Description

Example 1

The first step is as follows: adding 16 mmol of Zn (NO)₃)₂ · 6H₂Dissolving O in 120 mL of a mixed solvent of N, N-dimethylformamide (72 mL), ethanol (24 mL) and methanol (24 mL) to obtain a solution A; 64 mmol of 2-methylimidazole was dissolved in 40 mL of a mixed solvent of N, N-dimethylformamide (24 mL) and methanol (16 mL) to obtain a solution B. Mixing the solution A and the solution B, stirring at room temperature for 24 hours, then centrifugally washing the obtained product with methanol, and finally drying in a vacuum drying oven to obtain a ZIF-8 precursor; the second step is that: preparation of SbCl₃(7.5 mM) ethanol solution, adding 500 mg ZIF-8 precursor, soaking and stirring for 2 h, then centrifugally washing with ethanol, and drying in a vacuum drying oven for 12 h. The third step: grinding the obtained powder uniformly, placing the powder in the center of a tube furnace, and heating at a rate of 5 ℃ in Ar atmosphere^oHeating to 900 ℃ at C/min, annealing for 2 h, and pyrolyzing at high temperature to obtain the Sb/NC electrocatalyst.

In FIG. 1, Sb/NC-1 is an XRD pattern of the catalyst prepared in this example, and it can be seen that the obtained sample shows a broad diffraction peak only around 26 degrees, corresponding to the (002) peak of graphitized carbon, indicating that the ZIF-8 precursor has been successfully carbonized and partially graphitized. The transmission electron microscopy analysis of the obtained sample (fig. 2 a) can see that the sample presents a sheet-like morphology. The sample of this example was dispersed in a solvent and then dropped onto a rotating disk electrode to form a film on O₂ORR performance was tested in saturated 0.1M KOH solution. In FIG. 4, Sb/NC-1 is the LSV curve, and it can be seen that the half-wave potential of Sb/NC-1 is 0.86V vs. RHE and the limiting current density is 5.8 mA cm at 1600 rpm^-2And shows excellent ORR performance. FIG. 5 is a result of a ring plate test of the sample prepared in this example, and it can be seen from the graph that the number of transferred electrons of the Sb/NC-1 electrocatalyst in the oxygen reduction reaction is very close to the theoretical value of 4 and that its by-productionThe yield of the product is less than 8 percent and is very close to the commercial Pt/C, thereby proving high efficiency of the 4e^-And (4) an oxygen reduction process.

Example 2

The first step is as follows: adding 16 mmol of Zn (NO)₃)₂·6H₂Dissolving O in 120 mL of a mixed solvent of N, N-dimethylformamide (72 mL), ethanol (24 mL) and methanol (24 mL) to obtain a solution A; 64 mmol of 2-methylimidazole was dissolved in 40 mL of a mixed solvent of N, N-dimethylformamide (24 mL) and methanol (16 mL) to obtain a solution B. Mixing the solution A and the solution B, stirring at room temperature for 24 hours, then centrifugally washing the obtained product with methanol, and finally drying in a vacuum drying oven to obtain a ZIF-8 precursor; the second step is that: preparation of SbCl₃(8.5 mM) ethanol solution, adding 500 mg ZIF-8 precursor, soaking and stirring for 2 h, then centrifugally washing with ethanol, and drying in a vacuum drying oven for 12 h. The third step: and uniformly grinding the obtained powder, placing the powder in the center of a tube furnace, heating the powder to 900 ℃ at a heating rate of 5 ℃/min in Ar atmosphere, annealing the powder for 2 h, and performing high-temperature pyrolysis to obtain the Sb/NC electrocatalyst.

In FIG. 1, Sb/NC-2 is the XRD pattern of the catalyst prepared in this example, which is the same as that of example 1 and is located at 26^oThe broader diffraction peaks on the left and right correspond to the (002) peak of graphitized carbon. Further transmission electron microscopy analysis (as shown in fig. 2 b) is performed on the obtained sample, and the sample is also observed to have a sheet-like morphology. FIG. 3a is N of the sample₂A desorption curve, the specific surface area of Sb/NC-2 is calculated to be as high as 1321.8 m g^-1. Further, from the pore size distribution of FIG. 3b, it is seen that SbCl is present in comparison to the absence of SbCl₃The medium pores of the treated pure NC, Sb/NC-2 are obviously increased, and the total pore volume of the material is also increased from 0.67 m³ g^-1(NC) increase to 1.72 m³g^-1. The high specific surface area and porosity of Sb/NC-2 are important for improving the utilization efficiency of catalytic active sites, enhancing the mass transfer rate of reaction substrates and catalytic products on electrode interfaces and finally improving the ORR performance of the material. The slurry was prepared from this sample by rotating a disk electrode (RDE) at O₂Its ORR performance was tested in saturated 0.1M KOH solution. Sb/NC-2 in FIG. 4 isThe LSV curve shows that at 1600 rpm, the half-wave potential is 0.87V vs. RHE, and the limiting current density is 6.02 mA cm^-2Also, excellent ORR performance was exhibited. FIG. 5 shows the results of the ring disk test of the samples prepared under this example, which shows that the Sb/NC-2 electrocatalyst has a number of transferred electrons approaching the theoretical value of 4 in the oxygen reduction reaction, and its byproduct yield is less than 10%, very close to that of the commercial Pt/C, thus proving its high efficiency of 4e^-And (4) an oxygen reduction process. FIG. 6 is a graph of ORR stability for the samples prepared under this example, from which it can be seen that the Sb/NC-2 current decays only by 11% and the commercial Pt/C decays by 23% after 6000s at 1600 rpm, indicating that the samples have excellent oxygen reduction stability.

Example 3

The first step is as follows: adding 16 mmol of Zn (NO)₃)₂ · 6H₂Dissolving O in 120 mL of a mixed solvent of N, N-dimethylformamide (72 mL), ethanol (24 mL) and methanol (24 mL) to obtain a solution A; 64 mmol of 2-methylimidazole was dissolved in 40 mL of a mixed solvent of N, N-dimethylformamide (24 mL) and methanol (16 mL) to obtain a solution B. Mixing the solution A and the solution B, stirring at room temperature for 24 hours, then centrifugally washing the obtained product with methanol, and finally drying in a vacuum drying oven to obtain a ZIF-8 precursor; the second step is that: preparation of SbCl₃(9.0 mM) ethanol solution, adding 500 mg of ZIF-8 precursor, soaking and stirring for 2 h, then centrifugally washing with ethanol, and drying in a vacuum drying oven for 12 h. The third step: and uniformly grinding the obtained powder, placing the powder in the center of a tube furnace, heating the powder to 900 ℃ at a heating rate of 5 ℃/min in Ar atmosphere, annealing the powder for 2 h, and performing high-temperature pyrolysis to obtain the Sb/NC electrocatalyst.

In FIG. 1, Sb/NC-3 is the XRD pattern of the catalyst prepared in this example, the same as in examples 1 and 2, and is located at 26^oThe wider diffraction peaks on the left and right correspond to the (002) peak of graphitized carbon, and no diffraction peak with respect to Sb appears. The slurry was prepared from this sample by rotating a disk electrode (RDE) at O₂Its ORR performance was tested in saturated 0.1M KOH solution. Sb/NC-3 in FIG. 4 is the LSV curve thereof, and it can be seen that the half-wave potential thereof is 0.85 at 1600 rpmV vs. RHE, increase in limiting Current Density to 5.24 mA cm^-2And shows excellent ORR performance. FIG. 5 is a ring-disk test result of the sample prepared under this example, from which it can be seen that the number of transferred electrons of the Sb/NC electrocatalyst is close to the theoretical value of 4 in the oxygen reduction reaction, and its byproduct yield is less than 8%, very close to the commercial Pt/C, thus proving its high efficiency of 4e^-And (4) an oxygen reduction process.

If ZIF-8 is not passed through SbCl₃The NC electrocatalyst is obtained by direct high-temperature pyrolysis, the oxygen reduction LSV curve of the NC electrocatalyst is shown in figure 4, and the graph shows that the half-wave potential is only 0.78V vs. RHE and the limiting current density is 4.5 mA cm at 1600 rpm^-2The ORR performance is significantly poor.

If the ethanol solution of SbCl3 is changed to the ethanol solution of Bi (NO3) 3.5H 2O, other steps are not changed, and the Bi/NC electrocatalyst is obtained. Although Bi and Sb are the same group in the periodic table, the obtained Bi/NC electrocatalyst has a half-wave potential of only 0.76V vs. RHE at 1600 rpm and a limiting current density of 4.2 mA cm-2, and its ORR performance is much worse than that of Sb/NC.

If the ethanol solution of the SbCl3 is changed into the acetone solution of the SbCl3, and other steps are not changed, most of samples are evaporated in the high-temperature pyrolysis process, and the finally obtained catalyst has little yield and does not meet the actual application conditions;

if the ZIF-8 precursor is soaked in the SbCl3 ethanol solution for treatment, the ZIF-8 and the SbCl3 ethanol solution are mixed for treatment, and then the Sb/NC electrocatalyst is obtained through high-temperature pyrolysis. At 1600 rpm, the half-wave potential of the Sb/NC electrocatalyst obtained by blending is 0.83V vs. RHE, the limiting current density is 5.3 mA cm < -2 >, and the ORR performance is poorer compared with the soaking treatment.

If the steps of the first step and the third step are kept unchanged, SbCl is added₃When the amount of the catalyst is increased to 10 mM, most of the sample is evaporated in the high-temperature pyrolysis process, and the finally obtained catalyst has extremely low yield and does not meet the practical application condition.

Claims

1. The preparation method of the Sb/NC electrocatalyst is characterized by comprising the following preparation steps:

(1) adding Zn (NO)₃)₂·6H₂Dissolving O in a mixed solvent of N, N-dimethylformamide, ethanol and methanol to obtain a solution A; dissolving 2-methylimidazole in a mixed solvent of N, N-dimethylformamide and methanol to obtain a solution B, mixing the solution A and the solution B, stirring at room temperature, then centrifugally washing the obtained product with methanol, and finally drying in a vacuum drying oven to obtain a ZIF-8 precursor;

(2) preparation of a composition containing SbCl₃Adding a ZIF-8 precursor into the ethanol solution, soaking and stirring, then centrifugally washing with ethanol, and drying in a vacuum drying oven;

(3) and uniformly grinding the obtained powder, placing the powder in the center of a tube furnace, and carrying out high-temperature pyrolysis in Ar atmosphere to obtain the Sb/NC electrocatalyst.

2. The method of claim 1, wherein Zn (NO) is added to the Sb/NC electrocatalyst₃)₂·6H₂The molar concentration of O is 0.1-0.5 mmol/mL.

3. The method of claim 1, wherein the volume ratio of N, N-dimethylformamide, ethanol and methanol is 3: 0.8-1.2: 0.8-1.2.

4. The method of claim 1, wherein the concentration of 2-methylimidazole is 1-3 mmol/mL.

5. The method of claim 1, wherein the volume ratio of N, N dimethylformamide to methanol is 3: 1-2.

6. The method of claim 1, wherein SbCl is the product of the Sb/NC electrocatalyst₃The concentration of the ethanol solution of (2) is 7-9 mM.

7. The method of claim 1, wherein the inert atmosphere comprises Ar gas or nitrogen, and the tube furnace is heated to 800-900 ℃ at a heating rate of 5-6 ℃/min for annealing for 1-3 h.

8. Use of the Sb/NC electrocatalyst prepared according to any one of claims 1 to 7 as an oxygen reduction catalyst.